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 $69.98   10.506%   $77.3321   $77.33   $77.35   $77.30  
  Purchase #2 $234.65   11.783%   $262.2988   $262.30   $262.30   $262.30  
  Purchase #3 $176.77   3.776%   $183.4448   $183.44   $183.45   $183.40  
  Purchase #4 $242.29   10.717%   $268.2562   $268.26   $268.25   $268.30  
  Purchase #5 $203.95   4.715%   $213.5662   $213.57   $213.55   $213.60  
  Purchase #6 $209.27   7.267%   $224.4777   $224.48   $224.50   $224.50  
  Purchase #7 $191.82   8.377%   $207.8888   $207.89   $207.90   $207.90  
  7 purchase totals = $1,328.73       $1,437.2646   $1,437.27   $1,437.30   $1,437.30