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 $56.82   3.761%   $58.957   $58.96   $58.95   $59.00  
  Purchase #2 $136.89   10.639%   $151.4537   $151.45   $151.45   $151.50  
  Purchase #3 $118.57   11.623%   $132.3514   $132.35   $132.35   $132.40  
  Purchase #4 $30.31   13.496%   $34.4006   $34.40   $34.40   $34.40  
  Purchase #5 $99.67   7.786%   $107.4303   $107.43   $107.45   $107.40  
  Purchase #6 $113.25   9.644%   $124.1718   $124.17   $124.15   $124.20  
  Purchase #7 $136.61   12.318%   $153.4376   $153.44   $153.45   $153.40  
  7 purchase totals = $692.12       $762.2024   $762.20   $762.20   $762.30