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 $61.64   13.659%   $70.0594   $70.06   $70.05   $70.10  
  Purchase #2 $244.95   10.431%   $270.5007   $270.50   $270.50   $270.50  
  Purchase #3 $48.57   12.630%   $54.7044   $54.70   $54.70   $54.70  
  Purchase #4 $59.45   9.654%   $65.1893   $65.19   $65.20   $65.20  
  Purchase #5 $90.44   5.532%   $95.4431   $95.44   $95.45   $95.40  
  Purchase #6 $74.70   13.608%   $84.8652   $84.87   $84.85   $84.90  
  Purchase #7 $219.78   3.691%   $227.8921   $227.89   $227.90   $227.90  
  7 purchase totals = $799.53       $868.6542   $868.65   $868.65   $868.70