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 $204.55   11.115%   $227.2857   $227.29   $227.30   $227.30  
  Purchase #2 $116.49   7.605%   $125.3491   $125.35   $125.35   $125.30  
  Purchase #3 $209.48   10.495%   $231.4649   $231.46   $231.45   $231.50  
  Purchase #4 $49.68   6.841%   $53.0786   $53.08   $53.10   $53.10  
  Purchase #5 $244.61   13.599%   $277.8745   $277.87   $277.85   $277.90  
  Purchase #6 $82.78   12.798%   $93.3742   $93.37   $93.35   $93.40  
  Purchase #7 $232.89   5.350%   $245.3496   $245.35   $245.35   $245.30  
  7 purchase totals = $1,140.48       $1,253.7766   $1,253.77   $1,253.75   $1,253.80