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 $229.65   7.826%   $247.6224   $247.62   $247.60   $247.60  
  Purchase #2 $204.49   6.210%   $217.1888   $217.19   $217.20   $217.20  
  Purchase #3 $163.45   10.290%   $180.269   $180.27   $180.25   $180.30  
  Purchase #4 $91.52   12.677%   $103.122   $103.12   $103.10   $103.10  
  Purchase #5 $51.55   4.143%   $53.6857   $53.69   $53.70   $53.70  
  Purchase #6 $106.74   12.674%   $120.2682   $120.27   $120.25   $120.30  
  Purchase #7 $27.93   6.826%   $29.8365   $29.84   $29.85   $29.80  
  7 purchase totals = $875.33       $951.9926   $952.00   $951.95   $952.00