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 $76.36   9.131%   $83.3324   $83.33   $83.35   $83.30  
  Purchase #2 $135.57   10.234%   $149.4442   $149.44   $149.45   $149.40  
  Purchase #3 $112.68   11.362%   $125.4827   $125.48   $125.50   $125.50  
  Purchase #4 $165.37   10.722%   $183.101   $183.10   $183.10   $183.10  
  Purchase #5 $192.70   4.626%   $201.6143   $201.61   $201.60   $201.60  
  Purchase #6 $139.70   9.594%   $153.1028   $153.10   $153.10   $153.10  
  Purchase #7 $60.47   11.666%   $67.5244   $67.52   $67.50   $67.50  
  7 purchase totals = $882.85       $963.6018   $963.58   $963.60   $963.50