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 $117.75   7.713%   $126.8321   $126.83   $126.85   $126.80  
  Purchase #2 $73.40   5.718%   $77.597   $77.60   $77.60   $77.60  
  Purchase #3 $91.72   7.492%   $98.5917   $98.59   $98.60   $98.60  
  Purchase #4 $246.51   6.301%   $262.0426   $262.04   $262.05   $262.00  
  Purchase #5 $241.39   3.293%   $249.339   $249.34   $249.35   $249.30  
  Purchase #6 $55.25   3.384%   $57.1197   $57.12   $57.10   $57.10  
  Purchase #7 $166.65   4.118%   $173.5126   $173.51   $173.50   $173.50  
  7 purchase totals = $992.67       $1,045.0347   $1,045.03   $1,045.05   $1,044.90