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 $58.53   8.856%   $63.7134   $63.71   $63.70   $63.70  
  Purchase #2 $219.73   6.276%   $233.5203   $233.52   $233.50   $233.50  
  Purchase #3 $197.55   3.373%   $204.2134   $204.21   $204.20   $204.20  
  Purchase #4 $183.73   12.382%   $206.4794   $206.48   $206.50   $206.50  
  Purchase #5 $29.50   3.123%   $30.4213   $30.42   $30.40   $30.40  
  Purchase #6 $84.88   3.590%   $87.9272   $87.93   $87.95   $87.90  
  Purchase #7 $193.80   11.448%   $215.9862   $215.99   $216.00   $216.00  
  7 purchase totals = $967.72       $1,042.2612   $1,042.26   $1,042.25   $1,042.20