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 $91.28   11.442%   $101.7243   $101.72   $101.70   $101.70  
  Purchase #2 $240.59   12.141%   $269.8   $269.80   $269.80   $269.80  
  Purchase #3 $41.93   6.498%   $44.6546   $44.65   $44.65   $44.70  
  Purchase #4 $64.57   11.874%   $72.237   $72.24   $72.25   $72.20  
  Purchase #5 $61.90   10.313%   $68.2837   $68.28   $68.30   $68.30  
  Purchase #6 $207.64   5.300%   $218.6449   $218.64   $218.65   $218.60  
  Purchase #7 $52.90   5.179%   $55.6397   $55.64   $55.65   $55.60  
  7 purchase totals = $760.81       $830.9842   $830.97   $831.00   $830.90