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 $208.26   7.646%   $224.1836   $224.18   $224.20   $224.20  
  Purchase #2 $165.94   9.690%   $182.0196   $182.02   $182.00   $182.00  
  Purchase #3 $52.84   11.366%   $58.8458   $58.85   $58.85   $58.80  
  Purchase #4 $194.78   9.255%   $212.8069   $212.81   $212.80   $212.80  
  Purchase #5 $231.29   5.238%   $243.405   $243.41   $243.40   $243.40  
  Purchase #6 $56.97   13.692%   $64.7703   $64.77   $64.75   $64.80  
  Purchase #7 $17.40   5.254%   $18.3142   $18.31   $18.30   $18.30  
  7 purchase totals = $927.48       $1,004.3454   $1,004.35   $1,004.30   $1,004.30