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 $50.86   13.602%   $57.778   $57.78   $57.80   $57.80  
  Purchase #2 $238.25   3.266%   $246.0312   $246.03   $246.05   $246.00  
  Purchase #3 $151.84   11.307%   $169.0085   $169.01   $169.00   $169.00  
  Purchase #4 $51.74   7.341%   $55.5382   $55.54   $55.55   $55.50  
  Purchase #5 $161.48   12.212%   $181.1999   $181.20   $181.20   $181.20  
  Purchase #6 $65.80   10.369%   $72.6228   $72.62   $72.60   $72.60  
  Purchase #7 $230.54   11.259%   $256.4965   $256.50   $256.50   $256.50  
  7 purchase totals = $950.51       $1,038.6751   $1,038.68   $1,038.70   $1,038.60