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 $92.52   6.752%   $98.767   $98.77   $98.75   $98.80  
  Purchase #2 $86.93   7.612%   $93.5471   $93.55   $93.55   $93.50  
  Purchase #3 $13.75   7.142%   $14.732   $14.73   $14.75   $14.70  
  Purchase #4 $103.36   10.809%   $114.5322   $114.53   $114.55   $114.50  
  Purchase #5 $203.94   6.480%   $217.1553   $217.16   $217.15   $217.20  
  Purchase #6 $22.66   6.774%   $24.195   $24.20   $24.20   $24.20  
  Purchase #7 $123.49   10.144%   $136.0168   $136.02   $136.00   $136.00  
  7 purchase totals = $646.65       $698.9454   $698.96   $698.95   $698.90