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 $56.97   8.166%   $61.6222   $61.62   $61.60   $61.60  
  Purchase #2 $241.71   12.609%   $272.1872   $272.19   $272.20   $272.20  
  Purchase #3 $115.73   6.758%   $123.551   $123.55   $123.55   $123.60  
  Purchase #4 $202.91   3.823%   $210.6672   $210.67   $210.65   $210.70  
  Purchase #5 $129.27   5.700%   $136.6384   $136.64   $136.65   $136.60  
  Purchase #6 $31.36   8.279%   $33.9563   $33.96   $33.95   $34.00  
  Purchase #7 $231.48   4.557%   $242.0285   $242.03   $242.05   $242.00  
  7 purchase totals = $1,009.43       $1,080.6508   $1,080.66   $1,080.65   $1,080.70