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 $65.95   4.109%   $68.6599   $68.66   $68.65   $68.70  
  Purchase #2 $84.26   11.755%   $94.1648   $94.16   $94.15   $94.20  
  Purchase #3 $124.51   7.261%   $133.5507   $133.55   $133.55   $133.60  
  Purchase #4 $247.28   12.627%   $278.504   $278.50   $278.50   $278.50  
  Purchase #5 $55.74   3.412%   $57.6418   $57.64   $57.65   $57.60  
  Purchase #6 $223.88   5.345%   $235.8464   $235.85   $235.85   $235.80  
  Purchase #7 $110.96   11.434%   $123.6472   $123.65   $123.65   $123.60  
  7 purchase totals = $912.58       $992.0148   $992.01   $992.00   $992.00