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 $84.66   8.614%   $91.9526   $91.95   $91.95   $92.00  
  Purchase #2 $27.49   10.452%   $30.3633   $30.36   $30.35   $30.40  
  Purchase #3 $184.58   3.429%   $190.9092   $190.91   $190.90   $190.90  
  Purchase #4 $227.40   11.672%   $253.9421   $253.94   $253.95   $253.90  
  Purchase #5 $142.61   10.701%   $157.8707   $157.87   $157.85   $157.90  
  Purchase #6 $221.98   3.482%   $229.7093   $229.71   $229.70   $229.70  
  Purchase #7 $43.88   6.707%   $46.823   $46.82   $46.80   $46.80  
  7 purchase totals = $932.60       $1,001.5702   $1,001.56   $1,001.50   $1,001.60