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 $157.96   5.706%   $166.9732   $166.97   $166.95   $167.00  
  Purchase #2 $228.74   11.369%   $254.7455   $254.75   $254.75   $254.70  
  Purchase #3 $83.97   4.801%   $88.0014   $88.00   $88.00   $88.00  
  Purchase #4 $46.89   4.227%   $48.872   $48.87   $48.85   $48.90  
  Purchase #5 $204.83   11.803%   $229.0061   $229.01   $229.00   $229.00  
  Purchase #6 $130.76   7.389%   $140.4219   $140.42   $140.40   $140.40  
  Purchase #7 $164.90   9.352%   $180.3214   $180.32   $180.30   $180.30  
  7 purchase totals = $1,018.05       $1,108.3415   $1,108.34   $1,108.25   $1,108.30