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 $55.57   8.542%   $60.3168   $60.32   $60.30   $60.30  
  Purchase #2 $64.64   5.673%   $68.307   $68.31   $68.30   $68.30  
  Purchase #3 $186.60   7.605%   $200.7909   $200.79   $200.80   $200.80  
  Purchase #4 $50.64   7.121%   $54.2461   $54.25   $54.25   $54.20  
  Purchase #5 $59.75   8.724%   $64.9626   $64.96   $64.95   $65.00  
  Purchase #6 $89.33   5.540%   $94.2789   $94.28   $94.30   $94.30  
  Purchase #7 $236.43   11.264%   $263.0615   $263.06   $263.05   $263.10  
  7 purchase totals = $742.96       $805.9638   $805.97   $805.95   $806.00