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 $83.54   12.255%   $93.7778   $93.78   $93.80   $93.80  
  Purchase #2 $143.98   4.169%   $149.9825   $149.98   $150.00   $150.00  
  Purchase #3 $69.97   5.241%   $73.6371   $73.64   $73.65   $73.60  
  Purchase #4 $245.76   11.862%   $274.9121   $274.91   $274.90   $274.90  
  Purchase #5 $172.48   9.701%   $189.2123   $189.21   $189.20   $189.20  
  Purchase #6 $208.37   7.796%   $224.6145   $224.61   $224.60   $224.60  
  Purchase #7 $200.43   4.783%   $210.0166   $210.02   $210.00   $210.00  
  7 purchase totals = $1,124.53       $1,216.1529   $1,216.15   $1,216.15   $1,216.10