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 $228.68   10.290%   $252.2112   $252.21   $252.20   $252.20  
  Purchase #2 $195.55   3.577%   $202.5448   $202.54   $202.55   $202.50  
  Purchase #3 $15.55   7.696%   $16.7467   $16.75   $16.75   $16.70  
  Purchase #4 $39.72   6.823%   $42.4301   $42.43   $42.45   $42.40  
  Purchase #5 $146.58   13.845%   $166.874   $166.87   $166.85   $166.90  
  Purchase #6 $237.61   3.354%   $245.5794   $245.58   $245.60   $245.60  
  Purchase #7 $202.78   12.201%   $227.5212   $227.52   $227.50   $227.50  
  7 purchase totals = $1,066.47       $1,153.9074   $1,153.90   $1,153.90   $1,153.80