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 $95.65   8.281%   $103.5708   $103.57   $103.55   $103.60  
  Purchase #2 $13.42   6.570%   $14.3017   $14.30   $14.30   $14.30  
  Purchase #3 $131.80   4.586%   $137.8443   $137.84   $137.85   $137.80  
  Purchase #4 $117.97   4.315%   $123.0604   $123.06   $123.05   $123.10  
  Purchase #5 $205.40   5.328%   $216.3437   $216.34   $216.35   $216.30  
  Purchase #6 $201.61   9.710%   $221.1863   $221.19   $221.20   $221.20  
  Purchase #7 $110.53   13.761%   $125.74   $125.74   $125.75   $125.70  
  7 purchase totals = $876.38       $942.0472   $942.04   $942.05   $942.00