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 $104.53   7.766%   $112.6478   $112.65   $112.65   $112.60  
  Purchase #2 $232.52   6.116%   $246.7409   $246.74   $246.75   $246.70  
  Purchase #3 $132.90   6.556%   $141.6129   $141.61   $141.60   $141.60  
  Purchase #4 $67.48   8.716%   $73.3616   $73.36   $73.35   $73.40  
  Purchase #5 $211.43   5.311%   $222.659   $222.66   $222.65   $222.70  
  Purchase #6 $146.33   5.158%   $153.8777   $153.88   $153.90   $153.90  
  Purchase #7 $75.53   5.314%   $79.5437   $79.54   $79.55   $79.50  
  7 purchase totals = $970.72       $1,030.4436   $1,030.44   $1,030.45   $1,030.40