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 $207.28   5.807%   $219.3167   $219.32   $219.30   $219.30  
  Purchase #2 $247.83   4.369%   $258.6577   $258.66   $258.65   $258.70  
  Purchase #3 $62.30   3.659%   $64.5796   $64.58   $64.60   $64.60  
  Purchase #4 $231.51   8.222%   $250.5448   $250.54   $250.55   $250.50  
  Purchase #5 $234.55   7.183%   $251.3977   $251.40   $251.40   $251.40  
  Purchase #6 $239.38   8.639%   $260.06   $260.06   $260.05   $260.10  
  Purchase #7 $61.33   7.390%   $65.8623   $65.86   $65.85   $65.90  
  7 purchase totals = $1,284.18       $1,370.4188   $1,370.42   $1,370.40   $1,370.50