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 $147.75   3.818%   $153.3911   $153.39   $153.40   $153.40  
  Purchase #2 $203.33   13.757%   $231.3021   $231.30   $231.30   $231.30  
  Purchase #3 $52.73   11.590%   $58.8414   $58.84   $58.85   $58.80  
  Purchase #4 $229.43   13.160%   $259.623   $259.62   $259.60   $259.60  
  Purchase #5 $157.95   8.547%   $171.45   $171.45   $171.45   $171.50  
  Purchase #6 $97.68   7.105%   $104.6202   $104.62   $104.60   $104.60  
  Purchase #7 $235.60   13.630%   $267.7123   $267.71   $267.70   $267.70  
  7 purchase totals = $1,124.47       $1,246.9401   $1,246.93   $1,246.90   $1,246.90