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 $96.97   7.220%   $103.9712   $103.97   $103.95   $104.00  
  Purchase #2 $176.98   4.323%   $184.6308   $184.63   $184.65   $184.60  
  Purchase #3 $133.52   9.829%   $146.6437   $146.64   $146.65   $146.60  
  Purchase #4 $34.35   4.134%   $35.77   $35.77   $35.75   $35.80  
  Purchase #5 $136.63   6.608%   $145.6585   $145.66   $145.65   $145.70  
  Purchase #6 $52.27   7.376%   $56.1254   $56.13   $56.15   $56.10  
  Purchase #7 $77.29   5.733%   $81.721   $81.72   $81.70   $81.70  
  7 purchase totals = $708.01       $754.5206   $754.52   $754.50   $754.50