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 $64.25   3.307%   $66.3747   $66.37   $66.35   $66.40  
  Purchase #2 $184.74   6.550%   $196.8405   $196.84   $196.85   $196.80  
  Purchase #3 $161.56   6.261%   $171.6753   $171.68   $171.70   $171.70  
  Purchase #4 $147.70   11.215%   $164.2646   $164.26   $164.25   $164.30  
  Purchase #5 $194.37   3.417%   $201.0116   $201.01   $201.00   $201.00  
  Purchase #6 $175.42   10.730%   $194.2426   $194.24   $194.25   $194.20  
  Purchase #7 $246.88   13.794%   $280.9346   $280.93   $280.95   $280.90  
  7 purchase totals = $1,174.92       $1,275.3439   $1,275.33   $1,275.35   $1,275.30