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 $70.63   3.857%   $73.3542   $73.35   $73.35   $73.40  
  Purchase #2 $177.48   11.547%   $197.9736   $197.97   $197.95   $198.00  
  Purchase #3 $120.52   3.859%   $125.1709   $125.17   $125.15   $125.20  
  Purchase #4 $229.99   10.830%   $254.8979   $254.90   $254.90   $254.90  
  Purchase #5 $79.63   10.334%   $87.859   $87.86   $87.85   $87.90  
  Purchase #6 $140.26   3.834%   $145.6376   $145.64   $145.65   $145.60  
  Purchase #7 $144.88   8.159%   $156.7008   $156.70   $156.70   $156.70  
  7 purchase totals = $963.39       $1,041.5940   $1,041.59   $1,041.55   $1,041.70