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 $159.99   5.834%   $169.3238   $169.32   $169.30   $169.30  
  Purchase #2 $29.47   10.501%   $32.5646   $32.56   $32.55   $32.60  
  Purchase #3 $187.31   11.584%   $209.008   $209.01   $209.00   $209.00  
  Purchase #4 $13.26   7.859%   $14.3021   $14.30   $14.30   $14.30  
  Purchase #5 $181.74   13.516%   $206.304   $206.30   $206.30   $206.30  
  Purchase #6 $52.94   5.407%   $55.8025   $55.80   $55.80   $55.80  
  Purchase #7 $197.40   10.303%   $217.7381   $217.74   $217.75   $217.70  
  7 purchase totals = $822.11       $905.0431   $905.03   $905.00   $905.00