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 $62.49   8.197%   $67.6123   $67.61   $67.60   $67.60  
  Purchase #2 $109.54   3.777%   $113.6773   $113.68   $113.70   $113.70  
  Purchase #3 $85.37   4.173%   $88.9325   $88.93   $88.95   $88.90  
  Purchase #4 $220.46   8.296%   $238.7494   $238.75   $238.75   $238.70  
  Purchase #5 $180.80   4.816%   $189.5073   $189.51   $189.50   $189.50  
  Purchase #6 $131.62   8.449%   $142.7406   $142.74   $142.75   $142.70  
  Purchase #7 $74.70   12.557%   $84.0801   $84.08   $84.10   $84.10  
  7 purchase totals = $864.98       $925.2995   $925.30   $925.35   $925.20