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 $53.86   11.765%   $60.1966   $60.20   $60.20   $60.20  
  Purchase #2 $37.58   3.138%   $38.7593   $38.76   $38.75   $38.80  
  Purchase #3 $121.36   12.535%   $136.5725   $136.57   $136.55   $136.60  
  Purchase #4 $224.93   6.761%   $240.1375   $240.14   $240.15   $240.10  
  Purchase #5 $181.41   11.634%   $202.5152   $202.52   $202.50   $202.50  
  Purchase #6 $112.27   12.547%   $126.3565   $126.36   $126.35   $126.40  
  Purchase #7 $194.96   7.634%   $209.8432   $209.84   $209.85   $209.80  
  7 purchase totals = $926.37       $1,014.3808   $1,014.39   $1,014.35   $1,014.40