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 $242.28   11.869%   $271.0362   $271.04   $271.05   $271.00  
  Purchase #2 $214.27   4.446%   $223.7964   $223.80   $223.80   $223.80  
  Purchase #3 $144.46   3.414%   $149.3919   $149.39   $149.40   $149.40  
  Purchase #4 $24.99   3.446%   $25.8512   $25.85   $25.85   $25.90  
  Purchase #5 $157.73   5.600%   $166.5629   $166.56   $166.55   $166.60  
  Purchase #6 $36.86   12.393%   $41.4281   $41.43   $41.45   $41.40  
  Purchase #7 $148.92   4.220%   $155.2044   $155.20   $155.20   $155.20  
  7 purchase totals = $969.51       $1,033.2711   $1,033.27   $1,033.30   $1,033.30