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 $241.52   13.459%   $274.0262   $274.03   $274.05   $274.00  
  Purchase #2 $187.80   3.148%   $193.7119   $193.71   $193.70   $193.70  
  Purchase #3 $151.82   5.420%   $160.0486   $160.05   $160.05   $160.00  
  Purchase #4 $133.78   11.569%   $149.257   $149.26   $149.25   $149.30  
  Purchase #5 $204.48   8.503%   $221.8669   $221.87   $221.85   $221.90  
  Purchase #6 $90.43   5.374%   $95.2897   $95.29   $95.30   $95.30  
  Purchase #7 $64.88   3.606%   $67.2196   $67.22   $67.20   $67.20  
  7 purchase totals = $1,074.71       $1,161.4199   $1,161.43   $1,161.40   $1,161.40