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 $63.89   11.448%   $71.2041   $71.20   $71.20   $71.20  
  Purchase #2 $151.91   7.714%   $163.6283   $163.63   $163.65   $163.60  
  Purchase #3 $150.47   4.436%   $157.1448   $157.14   $157.15   $157.10  
  Purchase #4 $241.65   11.802%   $270.1695   $270.17   $270.15   $270.20  
  Purchase #5 $31.76   7.566%   $34.163   $34.16   $34.15   $34.20  
  Purchase #6 $185.80   9.852%   $204.105   $204.11   $204.10   $204.10  
  Purchase #7 $230.37   7.224%   $247.0119   $247.01   $247.00   $247.00  
  7 purchase totals = $1,055.85       $1,147.4266   $1,147.42   $1,147.40   $1,147.40