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 $56.85   8.116%   $61.4639   $61.46   $61.45   $61.50  
  Purchase #2 $128.31   13.772%   $145.9809   $145.98   $146.00   $146.00  
  Purchase #3 $219.49   3.715%   $227.6441   $227.64   $227.65   $227.60  
  Purchase #4 $59.98   8.783%   $65.248   $65.25   $65.25   $65.20  
  Purchase #5 $92.32   4.319%   $96.3073   $96.31   $96.30   $96.30  
  Purchase #6 $27.95   12.176%   $31.3532   $31.35   $31.35   $31.40  
  Purchase #7 $151.47   7.698%   $163.1302   $163.13   $163.15   $163.10  
  7 purchase totals = $736.37       $791.1276   $791.12   $791.15   $791.10