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 $70.98   7.138%   $76.0466   $76.05   $76.05   $76.00  
  Purchase #2 $200.42   11.243%   $222.9532   $222.95   $222.95   $223.00  
  Purchase #3 $90.31   13.337%   $102.3546   $102.35   $102.35   $102.40  
  Purchase #4 $67.33   4.295%   $70.2218   $70.22   $70.20   $70.20  
  Purchase #5 $45.97   11.151%   $51.0961   $51.10   $51.10   $51.10  
  Purchase #6 $66.82   4.798%   $70.026   $70.03   $70.05   $70.00  
  Purchase #7 $240.52   10.122%   $264.8654   $264.87   $264.85   $264.90  
  7 purchase totals = $782.35       $857.5637   $857.57   $857.55   $857.60