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 $214.99   5.211%   $226.1931   $226.19   $226.20   $226.20  
  Purchase #2 $211.55   3.603%   $219.1721   $219.17   $219.15   $219.20  
  Purchase #3 $5.88   3.238%   $6.0704   $6.07   $6.05   $6.10  
  Purchase #4 $66.41   4.541%   $69.4257   $69.43   $69.45   $69.40  
  Purchase #5 $247.62   9.769%   $271.81   $271.81   $271.80   $271.80  
  Purchase #6 $54.47   10.208%   $60.0303   $60.03   $60.05   $60.00  
  Purchase #7 $117.45   3.143%   $121.1415   $121.14   $121.15   $121.10  
  7 purchase totals = $918.37       $973.8431   $973.84   $973.85   $973.80