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 $207.68   12.824%   $234.3129   $234.31   $234.30   $234.30  
  Purchase #2 $209.58   9.412%   $229.3057   $229.31   $229.30   $229.30  
  Purchase #3 $223.73   9.334%   $244.613   $244.61   $244.60   $244.60  
  Purchase #4 $61.57   3.355%   $63.6357   $63.64   $63.65   $63.60  
  Purchase #5 $130.43   4.308%   $136.0489   $136.05   $136.05   $136.00  
  Purchase #6 $70.53   6.141%   $74.8612   $74.86   $74.85   $74.90  
  Purchase #7 $218.57   12.835%   $246.6235   $246.62   $246.60   $246.60  
  7 purchase totals = $1,122.09       $1,229.4009   $1,229.40   $1,229.35   $1,229.30