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 $193.48   7.486%   $207.9639   $207.96   $207.95   $208.00  
  Purchase #2 $113.57   10.721%   $125.7458   $125.75   $125.75   $125.70  
  Purchase #3 $34.94   6.442%   $37.1908   $37.19   $37.20   $37.20  
  Purchase #4 $148.49   4.583%   $155.2953   $155.30   $155.30   $155.30  
  Purchase #5 $16.59   4.463%   $17.3304   $17.33   $17.35   $17.30  
  Purchase #6 $159.98   13.751%   $181.9788   $181.98   $182.00   $182.00  
  Purchase #7 $135.59   3.118%   $139.8177   $139.82   $139.80   $139.80  
  7 purchase totals = $802.64       $865.3227   $865.33   $865.35   $865.30