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 $84.96   13.214%   $96.1866   $96.19   $96.20   $96.20  
  Purchase #2 $120.43   10.587%   $133.1799   $133.18   $133.20   $133.20  
  Purchase #3 $90.26   3.374%   $93.3054   $93.31   $93.30   $93.30  
  Purchase #4 $182.55   9.706%   $200.2683   $200.27   $200.25   $200.30  
  Purchase #5 $7.83   6.446%   $8.3347   $8.33   $8.35   $8.30  
  Purchase #6 $117.96   10.580%   $130.4402   $130.44   $130.45   $130.40  
  Purchase #7 $83.56   12.751%   $94.2147   $94.21   $94.20   $94.20  
  7 purchase totals = $687.55       $755.9298   $755.93   $755.95   $755.90