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 $43.63   8.406%   $47.2975   $47.30   $47.30   $47.30  
  Purchase #2 $67.43   12.571%   $75.9066   $75.91   $75.90   $75.90  
  Purchase #3 $99.74   12.415%   $112.1227   $112.12   $112.10   $112.10  
  Purchase #4 $220.64   10.533%   $243.88   $243.88   $243.90   $243.90  
  Purchase #5 $49.84   9.355%   $54.5025   $54.50   $54.50   $54.50  
  Purchase #6 $219.41   5.263%   $230.9575   $230.96   $230.95   $231.00  
  Purchase #7 $167.99   9.463%   $183.8869   $183.89   $183.90   $183.90  
  7 purchase totals = $868.68       $948.5537   $948.56   $948.55   $948.60