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 $174.43   11.108%   $193.8057   $193.81   $193.80   $193.80  
  Purchase #2 $108.51   3.201%   $111.9834   $111.98   $112.00   $112.00  
  Purchase #3 $97.30   6.212%   $103.3443   $103.34   $103.35   $103.30  
  Purchase #4 $87.36   9.452%   $95.6173   $95.62   $95.60   $95.60  
  Purchase #5 $105.73   13.464%   $119.9655   $119.97   $119.95   $120.00  
  Purchase #6 $114.67   7.155%   $122.8746   $122.87   $122.85   $122.90  
  Purchase #7 $107.55   7.837%   $115.9787   $115.98   $116.00   $116.00  
  7 purchase totals = $795.55       $863.5695   $863.57   $863.55   $863.60