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 $194.42   3.210%   $200.6609   $200.66   $200.65   $200.70  
  Purchase #2 $199.42   3.779%   $206.9561   $206.96   $206.95   $207.00  
  Purchase #3 $247.38   6.153%   $262.6013   $262.60   $262.60   $262.60  
  Purchase #4 $155.60   11.500%   $173.494   $173.49   $173.50   $173.50  
  Purchase #5 $14.97   5.119%   $15.7363   $15.74   $15.75   $15.70  
  Purchase #6 $94.64   12.655%   $106.6167   $106.62   $106.60   $106.60  
  Purchase #7 $81.27   11.769%   $90.8347   $90.83   $90.85   $90.80  
  7 purchase totals = $987.70       $1,056.9000   $1,056.90   $1,056.90   $1,056.90