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 $71.47   8.763%   $77.7329   $77.73   $77.75   $77.70  
  Purchase #2 $219.38   7.295%   $235.3838   $235.38   $235.40   $235.40  
  Purchase #3 $161.75   11.464%   $180.293   $180.29   $180.30   $180.30  
  Purchase #4 $32.55   13.238%   $36.859   $36.86   $36.85   $36.90  
  Purchase #5 $250.90   9.462%   $274.6402   $274.64   $274.65   $274.60  
  Purchase #6 $212.97   8.153%   $230.3334   $230.33   $230.35   $230.30  
  Purchase #7 $145.55   5.683%   $153.8216   $153.82   $153.80   $153.80  
  7 purchase totals = $1,094.57       $1,189.0639   $1,189.05   $1,189.10   $1,189.00