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 $229.81   13.285%   $260.3403   $260.34   $260.35   $260.30  
  Purchase #2 $134.55   8.766%   $146.3447   $146.34   $146.35   $146.30  
  Purchase #3 $140.25   4.293%   $146.2709   $146.27   $146.25   $146.30  
  Purchase #4 $51.57   12.621%   $58.0786   $58.08   $58.10   $58.10  
  Purchase #5 $95.86   6.597%   $102.1839   $102.18   $102.20   $102.20  
  Purchase #6 $174.89   11.540%   $195.0723   $195.07   $195.05   $195.10  
  Purchase #7 $152.56   9.489%   $167.0364   $167.04   $167.05   $167.00  
  7 purchase totals = $979.49       $1,075.3271   $1,075.32   $1,075.35   $1,075.30