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 $93.89   11.790%   $104.9596   $104.96   $104.95   $105.00  
  Purchase #2 $226.81   6.839%   $242.3215   $242.32   $242.30   $242.30  
  Purchase #3 $68.74   8.836%   $74.8139   $74.81   $74.80   $74.80  
  Purchase #4 $150.67   7.640%   $162.1812   $162.18   $162.20   $162.20  
  Purchase #5 $14.49   11.686%   $16.1833   $16.18   $16.20   $16.20  
  Purchase #6 $98.97   9.293%   $108.1673   $108.17   $108.15   $108.20  
  Purchase #7 $88.26   4.782%   $92.4806   $92.48   $92.50   $92.50  
  7 purchase totals = $741.83       $801.1074   $801.10   $801.10   $801.20