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 $182.93   10.712%   $202.5255   $202.53   $202.55   $202.50  
  Purchase #2 $101.94   7.578%   $109.665   $109.67   $109.65   $109.70  
  Purchase #3 $41.79   5.553%   $44.1106   $44.11   $44.10   $44.10  
  Purchase #4 $161.80   4.500%   $169.081   $169.08   $169.10   $169.10  
  Purchase #5 $95.28   10.357%   $105.1481   $105.15   $105.15   $105.10  
  Purchase #6 $20.69   6.279%   $21.9891   $21.99   $22.00   $22.00  
  Purchase #7 $141.80   9.846%   $155.7616   $155.76   $155.75   $155.80  
  7 purchase totals = $746.23       $808.2809   $808.29   $808.30   $808.30