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 $143.77   6.448%   $153.0403   $153.04   $153.05   $153.00  
  Purchase #2 $211.62   12.253%   $237.5498   $237.55   $237.55   $237.50  
  Purchase #3 $53.40   13.634%   $60.6806   $60.68   $60.70   $60.70  
  Purchase #4 $168.51   6.412%   $179.3149   $179.31   $179.30   $179.30  
  Purchase #5 $87.78   6.231%   $93.2496   $93.25   $93.25   $93.20  
  Purchase #6 $57.36   13.249%   $64.9596   $64.96   $64.95   $65.00  
  Purchase #7 $200.43   7.118%   $214.6966   $214.70   $214.70   $214.70  
  7 purchase totals = $922.87       $1,003.4914   $1,003.49   $1,003.50   $1,003.40