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 $95.91   6.344%   $101.9945   $101.99   $102.00   $102.00  
  Purchase #2 $87.79   11.630%   $98   $98.00   $98.00   $98.00  
  Purchase #3 $223.90   6.264%   $237.9251   $237.93   $237.95   $237.90  
  Purchase #4 $94.89   6.785%   $101.3283   $101.33   $101.35   $101.30  
  Purchase #5 $225.69   12.272%   $253.3867   $253.39   $253.40   $253.40  
  Purchase #6 $124.98   9.451%   $136.7919   $136.79   $136.80   $136.80  
  Purchase #7 $241.37   12.691%   $272.0023   $272.00   $272.00   $272.00  
  7 purchase totals = $1,094.53       $1,201.4288   $1,201.43   $1,201.50   $1,201.40