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 $203.77   9.347%   $222.8164   $222.82   $222.80   $222.80  
  Purchase #2 $109.63   8.826%   $119.3059   $119.31   $119.30   $119.30  
  Purchase #3 $70.55   9.534%   $77.2762   $77.28   $77.30   $77.30  
  Purchase #4 $22.79   7.200%   $24.4309   $24.43   $24.45   $24.40  
  Purchase #5 $145.95   6.452%   $155.3667   $155.37   $155.35   $155.40  
  Purchase #6 $98.64   11.336%   $109.8218   $109.82   $109.80   $109.80  
  Purchase #7 $218.83   12.698%   $246.617   $246.62   $246.60   $246.60  
  7 purchase totals = $870.16       $955.6349   $955.65   $955.60   $955.60