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 $242.57   9.498%   $265.6093   $265.61   $265.60   $265.60  
  Purchase #2 $163.43   8.277%   $176.9571   $176.96   $176.95   $177.00  
  Purchase #3 $150.52   7.186%   $161.3364   $161.34   $161.35   $161.30  
  Purchase #4 $85.64   10.696%   $94.8001   $94.80   $94.80   $94.80  
  Purchase #5 $117.28   9.421%   $128.3289   $128.33   $128.35   $128.30  
  Purchase #6 $68.65   3.478%   $71.0376   $71.04   $71.05   $71.00  
  Purchase #7 $64.75   11.216%   $72.0124   $72.01   $72.00   $72.00  
  7 purchase totals = $892.84       $970.0818   $970.09   $970.10   $970.00