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 $201.41   12.772%   $227.1341   $227.13   $227.15   $227.10  
  Purchase #2 $241.94   8.373%   $262.1976   $262.20   $262.20   $262.20  
  Purchase #3 $212.36   3.251%   $219.2638   $219.26   $219.25   $219.30  
  Purchase #4 $170.44   10.396%   $188.1589   $188.16   $188.15   $188.20  
  Purchase #5 $222.71   4.588%   $232.9279   $232.93   $232.95   $232.90  
  Purchase #6 $69.95   6.704%   $74.6394   $74.64   $74.65   $74.60  
  Purchase #7 $157.45   13.670%   $178.9734   $178.97   $178.95   $179.00  
  7 purchase totals = $1,276.26       $1,383.2951   $1,383.29   $1,383.30   $1,383.30