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 $233.91   10.551%   $258.5898   $258.59   $258.60   $258.60  
  Purchase #2 $219.30   3.156%   $226.2211   $226.22   $226.20   $226.20  
  Purchase #3 $113.51   11.188%   $126.2095   $126.21   $126.20   $126.20  
  Purchase #4 $112.54   4.461%   $117.5604   $117.56   $117.55   $117.60  
  Purchase #5 $234.55   11.127%   $260.6484   $260.65   $260.65   $260.60  
  Purchase #6 $24.97   8.666%   $27.1339   $27.13   $27.15   $27.10  
  Purchase #7 $44.84   13.165%   $50.7432   $50.74   $50.75   $50.70  
  7 purchase totals = $983.62       $1,067.1063   $1,067.10   $1,067.10   $1,067.00