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 $55.96   12.513%   $62.9623   $62.96   $62.95   $63.00  
  Purchase #2 $235.49   13.261%   $266.7183   $266.72   $266.70   $266.70  
  Purchase #3 $148.26   12.681%   $167.0609   $167.06   $167.05   $167.10  
  Purchase #4 $176.35   8.324%   $191.0294   $191.03   $191.05   $191.00  
  Purchase #5 $28.31   4.123%   $29.4772   $29.48   $29.50   $29.50  
  Purchase #6 $186.62   13.177%   $211.2109   $211.21   $211.20   $211.20  
  Purchase #7 $146.70   3.173%   $151.3548   $151.35   $151.35   $151.40  
  7 purchase totals = $977.69       $1,079.8138   $1,079.81   $1,079.80   $1,079.90