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 $54.64   11.473%   $60.9088   $60.91   $60.90   $60.90  
  Purchase #2 $240.88   9.811%   $264.5127   $264.51   $264.50   $264.50  
  Purchase #3 $245.35   10.730%   $271.6761   $271.68   $271.70   $271.70  
  Purchase #4 $197.90   6.844%   $211.4443   $211.44   $211.45   $211.40  
  Purchase #5 $5.69   3.640%   $5.8971   $5.90   $5.90   $5.90  
  Purchase #6 $174.54   10.639%   $193.1093   $193.11   $193.10   $193.10  
  Purchase #7 $155.70   4.359%   $162.487   $162.49   $162.50   $162.50  
  7 purchase totals = $1,074.70       $1,170.0353   $1,170.04   $1,170.05   $1,170.00