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 $162.29   11.594%   $181.1059   $181.11   $181.10   $181.10  
  Purchase #2 $158.44   7.575%   $170.4418   $170.44   $170.45   $170.40  
  Purchase #3 $156.53   11.549%   $174.6076   $174.61   $174.60   $174.60  
  Purchase #4 $59.38   4.363%   $61.9707   $61.97   $61.95   $62.00  
  Purchase #5 $242.50   7.287%   $260.171   $260.17   $260.15   $260.20  
  Purchase #6 $121.77   8.873%   $132.5747   $132.57   $132.55   $132.60  
  Purchase #7 $23.47   5.740%   $24.8172   $24.82   $24.80   $24.80  
  7 purchase totals = $924.38       $1,005.6889   $1,005.69   $1,005.60   $1,005.70