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 $7.75   4.413%   $8.092   $8.09   $8.10   $8.10  
  Purchase #2 $137.51   5.510%   $145.0868   $145.09   $145.10   $145.10  
  Purchase #3 $149.61   7.171%   $160.3385   $160.34   $160.35   $160.30  
  Purchase #4 $209.80   9.614%   $229.9702   $229.97   $229.95   $230.00  
  Purchase #5 $117.27   11.126%   $130.3175   $130.32   $130.30   $130.30  
  Purchase #6 $158.88   13.552%   $180.4114   $180.41   $180.40   $180.40  
  Purchase #7 $54.82   6.250%   $58.2463   $58.25   $58.25   $58.20  
  7 purchase totals = $835.64       $912.4627   $912.47   $912.45   $912.40