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 $52.27   6.523%   $55.6796   $55.68   $55.70   $55.70  
  Purchase #2 $148.82   9.356%   $162.7436   $162.74   $162.75   $162.70  
  Purchase #3 $88.64   7.639%   $95.4112   $95.41   $95.40   $95.40  
  Purchase #4 $232.75   8.541%   $252.6292   $252.63   $252.65   $252.60  
  Purchase #5 $248.72   9.490%   $272.3235   $272.32   $272.30   $272.30  
  Purchase #6 $95.73   7.223%   $102.6446   $102.64   $102.65   $102.60  
  Purchase #7 $11.50   6.601%   $12.2591   $12.26   $12.25   $12.30  
  7 purchase totals = $878.43       $953.6908   $953.68   $953.70   $953.60