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 $131.67   5.821%   $139.3345   $139.33   $139.35   $139.30  
  Purchase #2 $25.86   3.452%   $26.7527   $26.75   $26.75   $26.80  
  Purchase #3 $165.66   12.784%   $186.838   $186.84   $186.85   $186.80  
  Purchase #4 $112.81   4.142%   $117.4826   $117.48   $117.50   $117.50  
  Purchase #5 $229.48   5.266%   $241.5644   $241.56   $241.55   $241.60  
  Purchase #6 $57.34   11.867%   $64.1445   $64.14   $64.15   $64.10  
  Purchase #7 $154.60   4.221%   $161.1257   $161.13   $161.15   $161.10  
  7 purchase totals = $877.42       $937.2424   $937.23   $937.30   $937.20