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 $66.96   3.743%   $69.4663   $69.47   $69.45   $69.50  
  Purchase #2 $187.91   8.583%   $204.0383   $204.04   $204.05   $204.00  
  Purchase #3 $241.35   5.188%   $253.8712   $253.87   $253.85   $253.90  
  Purchase #4 $121.60   3.120%   $125.3939   $125.39   $125.40   $125.40  
  Purchase #5 $97.44   8.411%   $105.6357   $105.64   $105.65   $105.60  
  Purchase #6 $93.99   13.207%   $106.4033   $106.40   $106.40   $106.40  
  Purchase #7 $145.63   3.417%   $150.6062   $150.61   $150.60   $150.60  
  7 purchase totals = $954.88       $1,015.4149   $1,015.42   $1,015.40   $1,015.40