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 $32.69   11.288%   $36.38   $36.38   $36.40   $36.40  
  Purchase #2 $57.83   5.226%   $60.8522   $60.85   $60.85   $60.90  
  Purchase #3 $55.33   3.152%   $57.074   $57.07   $57.05   $57.10  
  Purchase #4 $159.26   8.390%   $172.6219   $172.62   $172.60   $172.60  
  Purchase #5 $170.81   6.237%   $181.4634   $181.46   $181.45   $181.50  
  Purchase #6 $250.35   8.328%   $271.1991   $271.20   $271.20   $271.20  
  Purchase #7 $226.84   8.234%   $245.518   $245.52   $245.50   $245.50  
  7 purchase totals = $953.11       $1,025.1086   $1,025.10   $1,025.05   $1,025.20