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 $152.53   10.522%   $168.5792   $168.58   $168.60   $168.60  
  Purchase #2 $120.97   4.442%   $126.3435   $126.34   $126.35   $126.30  
  Purchase #3 $171.26   4.804%   $179.4873   $179.49   $179.50   $179.50  
  Purchase #4 $63.29   3.447%   $65.4716   $65.47   $65.45   $65.50  
  Purchase #5 $62.97   7.558%   $67.7293   $67.73   $67.75   $67.70  
  Purchase #6 $96.74   5.831%   $102.3809   $102.38   $102.40   $102.40  
  Purchase #7 $110.82   5.532%   $116.9506   $116.95   $116.95   $117.00  
  7 purchase totals = $778.58       $826.9424   $826.94   $827.00   $827.00