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 $32.72   6.472%   $34.8376   $34.84   $34.85   $34.80  
  Purchase #2 $225.25   11.731%   $251.6741   $251.67   $251.65   $251.70  
  Purchase #3 $244.69   6.255%   $259.9954   $260.00   $260.00   $260.00  
  Purchase #4 $132.97   10.336%   $146.7138   $146.71   $146.70   $146.70  
  Purchase #5 $53.72   3.845%   $55.7855   $55.79   $55.80   $55.80  
  Purchase #6 $50.55   3.551%   $52.345   $52.35   $52.35   $52.30  
  Purchase #7 $216.69   6.521%   $230.8204   $230.82   $230.80   $230.80  
  7 purchase totals = $956.59       $1,032.1718   $1,032.18   $1,032.15   $1,032.10