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 $235.69   12.338%   $264.7694   $264.77   $264.75   $264.80  
  Purchase #2 $10.38   13.271%   $11.7575   $11.76   $11.75   $11.80  
  Purchase #3 $155.46   3.755%   $161.2975   $161.30   $161.30   $161.30  
  Purchase #4 $160.60   11.642%   $179.2971   $179.30   $179.30   $179.30  
  Purchase #5 $194.85   3.327%   $201.3327   $201.33   $201.35   $201.30  
  Purchase #6 $49.42   11.424%   $55.0657   $55.07   $55.05   $55.10  
  Purchase #7 $195.96   13.295%   $222.0129   $222.01   $222.00   $222.00  
  7 purchase totals = $1,002.36       $1,095.5328   $1,095.54   $1,095.50   $1,095.60