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 $157.89   3.430%   $163.3056   $163.31   $163.30   $163.30  
  Purchase #2 $16.29   11.723%   $18.1997   $18.20   $18.20   $18.20  
  Purchase #3 $191.49   4.512%   $200.13   $200.13   $200.15   $200.10  
  Purchase #4 $85.72   4.804%   $89.838   $89.84   $89.85   $89.80  
  Purchase #5 $70.25   5.852%   $74.361   $74.36   $74.35   $74.40  
  Purchase #6 $206.80   10.270%   $228.0384   $228.04   $228.05   $228.00  
  Purchase #7 $153.34   3.334%   $158.4524   $158.45   $158.45   $158.50  
  7 purchase totals = $881.78       $932.3251   $932.33   $932.35   $932.30