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 $58.34   8.542%   $63.3234   $63.32   $63.30   $63.30  
  Purchase #2 $59.43   4.341%   $62.0099   $62.01   $62.00   $62.00  
  Purchase #3 $132.56   5.787%   $140.2312   $140.23   $140.25   $140.20  
  Purchase #4 $65.29   11.630%   $72.8832   $72.88   $72.90   $72.90  
  Purchase #5 $216.84   10.749%   $240.1481   $240.15   $240.15   $240.10  
  Purchase #6 $84.93   4.516%   $88.7654   $88.77   $88.75   $88.80  
  Purchase #7 $121.36   13.416%   $137.6417   $137.64   $137.65   $137.60  
  7 purchase totals = $738.75       $805.0029   $805.00   $805.00   $804.90