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 $238.46   12.171%   $267.483   $267.48   $267.50   $267.50  
  Purchase #2 $44.34   7.659%   $47.736   $47.74   $47.75   $47.70  
  Purchase #3 $106.68   6.741%   $113.8713   $113.87   $113.85   $113.90  
  Purchase #4 $59.97   11.700%   $66.9865   $66.99   $67.00   $67.00  
  Purchase #5 $27.76   8.504%   $30.1207   $30.12   $30.10   $30.10  
  Purchase #6 $124.80   8.638%   $135.5802   $135.58   $135.60   $135.60  
  Purchase #7 $204.63   12.207%   $229.6092   $229.61   $229.60   $229.60  
  7 purchase totals = $806.64       $891.3869   $891.39   $891.40   $891.40