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 $241.81   5.132%   $254.2197   $254.22   $254.20   $254.20  
  Purchase #2 $96.79   8.855%   $105.3608   $105.36   $105.35   $105.40  
  Purchase #3 $160.30   6.368%   $170.5079   $170.51   $170.50   $170.50  
  Purchase #4 $205.73   6.186%   $218.4565   $218.46   $218.45   $218.50  
  Purchase #5 $205.83   10.178%   $226.7794   $226.78   $226.80   $226.80  
  Purchase #6 $202.76   5.444%   $213.7983   $213.80   $213.80   $213.80  
  Purchase #7 $7.75   12.443%   $8.7143   $8.71   $8.70   $8.70  
  7 purchase totals = $1,120.97       $1,197.8369   $1,197.84   $1,197.80   $1,197.90