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 $59.92   10.735%   $66.3524   $66.35   $66.35   $66.40  
  Purchase #2 $179.57   13.656%   $204.0921   $204.09   $204.10   $204.10  
  Purchase #3 $187.57   12.276%   $210.5961   $210.60   $210.60   $210.60  
  Purchase #4 $246.43   5.207%   $259.2616   $259.26   $259.25   $259.30  
  Purchase #5 $127.64   8.554%   $138.5583   $138.56   $138.55   $138.60  
  Purchase #6 $75.36   11.238%   $83.829   $83.83   $83.85   $83.80  
  Purchase #7 $185.84   10.584%   $205.5093   $205.51   $205.50   $205.50  
  7 purchase totals = $1,062.33       $1,168.1988   $1,168.20   $1,168.20   $1,168.30