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 $226.27   9.464%   $247.6842   $247.68   $247.70   $247.70  
  Purchase #2 $228.36   10.318%   $251.9222   $251.92   $251.90   $251.90  
  Purchase #3 $87.53   4.755%   $91.6921   $91.69   $91.70   $91.70  
  Purchase #4 $208.57   4.293%   $217.5239   $217.52   $217.50   $217.50  
  Purchase #5 $165.98   5.524%   $175.1487   $175.15   $175.15   $175.10  
  Purchase #6 $146.70   11.108%   $162.9954   $163.00   $163.00   $163.00  
  Purchase #7 $195.64   12.290%   $219.6842   $219.68   $219.70   $219.70  
  7 purchase totals = $1,259.05       $1,366.6507   $1,366.64   $1,366.65   $1,366.60