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 $62.59   3.638%   $64.867   $64.87   $64.85   $64.90  
  Purchase #2 $96.51   6.418%   $102.704   $102.70   $102.70   $102.70  
  Purchase #3 $193.70   5.481%   $204.3167   $204.32   $204.30   $204.30  
  Purchase #4 $116.93   5.348%   $123.1834   $123.18   $123.20   $123.20  
  Purchase #5 $41.35   13.671%   $47.003   $47.00   $47.00   $47.00  
  Purchase #6 $118.75   12.350%   $133.4156   $133.42   $133.40   $133.40  
  Purchase #7 $228.98   11.515%   $255.347   $255.35   $255.35   $255.30  
  7 purchase totals = $858.81       $930.8367   $930.84   $930.80   $930.80