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 $187.78   8.625%   $203.976   $203.98   $204.00   $204.00  
  Purchase #2 $123.75   7.781%   $133.379   $133.38   $133.40   $133.40  
  Purchase #3 $108.31   8.740%   $117.7763   $117.78   $117.80   $117.80  
  Purchase #4 $49.45   12.458%   $55.6105   $55.61   $55.60   $55.60  
  Purchase #5 $178.79   7.235%   $191.7255   $191.73   $191.75   $191.70  
  Purchase #6 $242.87   13.163%   $274.839   $274.84   $274.85   $274.80  
  Purchase #7 $89.95   4.152%   $93.6847   $93.68   $93.70   $93.70  
  7 purchase totals = $980.90       $1,070.9910   $1,071.00   $1,071.10   $1,071.00