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 $82.73   11.810%   $92.5004   $92.50   $92.50   $92.50  
  Purchase #2 $178.87   11.543%   $199.517   $199.52   $199.50   $199.50  
  Purchase #3 $176.54   8.584%   $191.6942   $191.69   $191.70   $191.70  
  Purchase #4 $218.43   4.818%   $228.954   $228.95   $228.95   $229.00  
  Purchase #5 $125.37   13.789%   $142.6573   $142.66   $142.65   $142.70  
  Purchase #6 $102.99   7.760%   $110.982   $110.98   $111.00   $111.00  
  Purchase #7 $244.94   12.453%   $275.4424   $275.44   $275.45   $275.40  
  7 purchase totals = $1,129.87       $1,241.7473   $1,241.74   $1,241.75   $1,241.80