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 $54.53   3.617%   $56.5024   $56.50   $56.50   $56.50  
  Purchase #2 $108.56   8.556%   $117.8484   $117.85   $117.85   $117.80  
  Purchase #3 $196.85   5.561%   $207.7968   $207.80   $207.80   $207.80  
  Purchase #4 $226.41   9.315%   $247.5001   $247.50   $247.50   $247.50  
  Purchase #5 $85.45   13.190%   $96.7209   $96.72   $96.70   $96.70  
  Purchase #6 $208.54   5.777%   $220.5874   $220.59   $220.60   $220.60  
  Purchase #7 $83.48   12.850%   $94.2072   $94.21   $94.20   $94.20  
  7 purchase totals = $963.82       $1,041.1632   $1,041.17   $1,041.15   $1,041.10