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 $61.56   5.559%   $64.9821   $64.98   $65.00   $65.00  
  Purchase #2 $179.72   11.284%   $199.9996   $200.00   $200.00   $200.00  
  Purchase #3 $65.90   7.571%   $70.8893   $70.89   $70.90   $70.90  
  Purchase #4 $176.65   10.811%   $195.7476   $195.75   $195.75   $195.70  
  Purchase #5 $113.87   6.668%   $121.4629   $121.46   $121.45   $121.50  
  Purchase #6 $153.95   9.788%   $169.0186   $169.02   $169.00   $169.00  
  Purchase #7 $46.43   10.577%   $51.3409   $51.34   $51.35   $51.30  
  7 purchase totals = $798.08       $873.4410   $873.44   $873.45   $873.40