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 $81.39   13.286%   $92.2035   $92.20   $92.20   $92.20  
  Purchase #2 $176.52   4.621%   $184.677   $184.68   $184.70   $184.70  
  Purchase #3 $28.57   6.668%   $30.475   $30.48   $30.50   $30.50  
  Purchase #4 $111.76   12.657%   $125.9055   $125.91   $125.90   $125.90  
  Purchase #5 $125.76   5.245%   $132.3561   $132.36   $132.35   $132.40  
  Purchase #6 $250.88   10.680%   $277.674   $277.67   $277.65   $277.70  
  Purchase #7 $227.29   6.256%   $241.5093   $241.51   $241.50   $241.50  
  7 purchase totals = $1,002.17       $1,084.8004   $1,084.81   $1,084.80   $1,084.90