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 $246.39   6.576%   $262.5926   $262.59   $262.60   $262.60  
  Purchase #2 $218.34   11.400%   $243.2308   $243.23   $243.25   $243.20  
  Purchase #3 $198.76   9.175%   $216.9962   $217.00   $217.00   $217.00  
  Purchase #4 $62.52   5.773%   $66.1293   $66.13   $66.15   $66.10  
  Purchase #5 $27.25   3.257%   $28.1375   $28.14   $28.15   $28.10  
  Purchase #6 $142.33   7.636%   $153.1983   $153.20   $153.20   $153.20  
  Purchase #7 $150.57   9.335%   $164.6257   $164.63   $164.65   $164.60  
  7 purchase totals = $1,046.16       $1,134.9104   $1,134.92   $1,135.00   $1,134.80