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 $246.38   3.114%   $254.0523   $254.05   $254.05   $254.10  
  Purchase #2 $97.64   3.133%   $100.6991   $100.70   $100.70   $100.70  
  Purchase #3 $7.98   13.317%   $9.0427   $9.04   $9.05   $9.00  
  Purchase #4 $216.91   8.421%   $235.176   $235.18   $235.20   $235.20  
  Purchase #5 $66.92   3.864%   $69.5058   $69.51   $69.50   $69.50  
  Purchase #6 $59.31   13.349%   $67.2273   $67.23   $67.25   $67.20  
  Purchase #7 $167.62   11.115%   $186.251   $186.25   $186.25   $186.30  
  7 purchase totals = $862.76       $921.9542   $921.96   $922.00   $922.00