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 $193.33   6.319%   $205.5465   $205.55   $205.55   $205.50  
  Purchase #2 $161.75   6.140%   $171.6815   $171.68   $171.70   $171.70  
  Purchase #3 $45.96   3.565%   $47.5985   $47.60   $47.60   $47.60  
  Purchase #4 $181.67   4.581%   $189.9923   $189.99   $190.00   $190.00  
  Purchase #5 $131.93   13.339%   $149.5281   $149.53   $149.55   $149.50  
  Purchase #6 $155.41   6.639%   $165.7277   $165.73   $165.75   $165.70  
  Purchase #7 $116.70   11.584%   $130.2185   $130.22   $130.20   $130.20  
  7 purchase totals = $986.75       $1,060.2931   $1,060.30   $1,060.35   $1,060.20