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 $103.35   10.608%   $114.3134   $114.31   $114.30   $114.30  
  Purchase #2 $194.91   5.156%   $204.9596   $204.96   $204.95   $205.00  
  Purchase #3 $15.32   12.272%   $17.2001   $17.20   $17.20   $17.20  
  Purchase #4 $150.64   12.335%   $169.2214   $169.22   $169.20   $169.20  
  Purchase #5 $193.62   6.191%   $205.607   $205.61   $205.60   $205.60  
  Purchase #6 $97.73   5.265%   $102.8755   $102.88   $102.90   $102.90  
  Purchase #7 $96.49   11.425%   $107.514   $107.51   $107.50   $107.50  
  7 purchase totals = $852.06       $921.6910   $921.69   $921.65   $921.70