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 $155.38   3.266%   $160.4547   $160.45   $160.45   $160.50  
  Purchase #2 $175.65   13.537%   $199.4277   $199.43   $199.45   $199.40  
  Purchase #3 $205.59   7.742%   $221.5068   $221.51   $221.50   $221.50  
  Purchase #4 $43.54   13.845%   $49.5681   $49.57   $49.55   $49.60  
  Purchase #5 $233.70   5.443%   $246.4203   $246.42   $246.40   $246.40  
  Purchase #6 $100.34   6.454%   $106.8159   $106.82   $106.80   $106.80  
  Purchase #7 $57.48   8.310%   $62.2566   $62.26   $62.25   $62.30  
  7 purchase totals = $971.68       $1,046.4501   $1,046.46   $1,046.40   $1,046.50