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 $59.72   7.742%   $64.3435   $64.34   $64.35   $64.30  
  Purchase #2 $137.34   13.368%   $155.6996   $155.70   $155.70   $155.70  
  Purchase #3 $177.26   13.802%   $201.7254   $201.73   $201.75   $201.70  
  Purchase #4 $239.46   13.617%   $272.0673   $272.07   $272.05   $272.10  
  Purchase #5 $19.62   13.163%   $22.2026   $22.20   $22.20   $22.20  
  Purchase #6 $112.32   7.263%   $120.4778   $120.48   $120.50   $120.50  
  Purchase #7 $190.25   7.547%   $204.6082   $204.61   $204.60   $204.60  
  7 purchase totals = $935.97       $1,041.1244   $1,041.13   $1,041.15   $1,041.10