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 $7.78   7.415%   $8.3569   $8.36   $8.35   $8.40  
  Purchase #2 $198.58   8.481%   $215.4216   $215.42   $215.40   $215.40  
  Purchase #3 $172.54   13.501%   $195.8346   $195.83   $195.85   $195.80  
  Purchase #4 $168.89   3.244%   $174.3688   $174.37   $174.35   $174.40  
  Purchase #5 $98.72   8.149%   $106.7647   $106.76   $106.75   $106.80  
  Purchase #6 $7.83   9.391%   $8.5653   $8.57   $8.55   $8.60  
  Purchase #7 $204.44   13.687%   $232.4217   $232.42   $232.40   $232.40  
  7 purchase totals = $858.78       $941.7336   $941.73   $941.65   $941.80