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 $85.69   12.221%   $96.1622   $96.16   $96.15   $96.20  
  Purchase #2 $227.72   9.457%   $249.2555   $249.26   $249.25   $249.30  
  Purchase #3 $221.67   7.522%   $238.344   $238.34   $238.35   $238.30  
  Purchase #4 $10.64   3.191%   $10.9795   $10.98   $11.00   $11.00  
  Purchase #5 $202.35   4.179%   $210.8062   $210.81   $210.80   $210.80  
  Purchase #6 $187.51   8.835%   $204.0765   $204.08   $204.10   $204.10  
  Purchase #7 $21.55   6.684%   $22.9904   $22.99   $23.00   $23.00  
  7 purchase totals = $957.13       $1,032.6143   $1,032.62   $1,032.65   $1,032.70