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 $87.41   6.540%   $93.1266   $93.13   $93.15   $93.10  
  Purchase #2 $217.91   12.560%   $245.2795   $245.28   $245.30   $245.30  
  Purchase #3 $209.36   13.315%   $237.2363   $237.24   $237.25   $237.20  
  Purchase #4 $27.76   5.655%   $29.3298   $29.33   $29.35   $29.30  
  Purchase #5 $206.79   7.667%   $222.6446   $222.64   $222.65   $222.60  
  Purchase #6 $147.27   3.126%   $151.8737   $151.87   $151.85   $151.90  
  Purchase #7 $97.51   9.531%   $106.8037   $106.80   $106.80   $106.80  
  7 purchase totals = $994.01       $1,086.2942   $1,086.29   $1,086.35   $1,086.20