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 $59.61   12.411%   $67.0082   $67.01   $67.00   $67.00  
  Purchase #2 $236.65   11.277%   $263.337   $263.34   $263.35   $263.30  
  Purchase #3 $59.27   7.334%   $63.6169   $63.62   $63.60   $63.60  
  Purchase #4 $193.40   4.826%   $202.7335   $202.73   $202.75   $202.70  
  Purchase #5 $155.95   10.206%   $171.8663   $171.87   $171.85   $171.90  
  Purchase #6 $130.50   10.311%   $143.9559   $143.96   $143.95   $144.00  
  Purchase #7 $221.58   11.359%   $246.7493   $246.75   $246.75   $246.70  
  7 purchase totals = $1,056.96       $1,159.2671   $1,159.28   $1,159.25   $1,159.20