Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $117.77   10.761%   $130.4432   $130.44   $130.45   $130.40  
  Purchase #2 $243.64   9.735%   $267.3584   $267.36   $267.35   $267.40  
  Purchase #3 $128.26   10.847%   $142.1724   $142.17   $142.15   $142.20  
  Purchase #4 $69.29   11.743%   $77.4267   $77.43   $77.45   $77.40  
  Purchase #5 $122.26   11.685%   $136.5461   $136.55   $136.55   $136.50  
  Purchase #6 $224.88   11.695%   $251.1797   $251.18   $251.20   $251.20  
  Purchase #7 $132.61   10.142%   $146.0593   $146.06   $146.05   $146.10  
  7 purchase totals = $1,038.71       $1,151.1858   $1,151.19   $1,151.20   $1,151.20