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 $153.45   13.868%   $174.7304   $174.73   $174.75   $174.70  
  Purchase #2 $167.32   6.701%   $178.5321   $178.53   $178.55   $178.50  
  Purchase #3 $56.56   6.355%   $60.1544   $60.15   $60.15   $60.20  
  Purchase #4 $92.40   6.344%   $98.2619   $98.26   $98.25   $98.30  
  Purchase #5 $98.36   5.326%   $103.5987   $103.60   $103.60   $103.60  
  Purchase #6 $239.45   3.317%   $247.3926   $247.39   $247.40   $247.40  
  Purchase #7 $54.74   7.335%   $58.7552   $58.76   $58.75   $58.80  
  7 purchase totals = $862.28       $921.4253   $921.42   $921.45   $921.50