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 $60.54   11.374%   $67.4258   $67.43   $67.45   $67.40  
  Purchase #2 $231.89   6.606%   $247.2087   $247.21   $247.20   $247.20  
  Purchase #3 $205.88   7.721%   $221.776   $221.78   $221.80   $221.80  
  Purchase #4 $43.73   13.851%   $49.787   $49.79   $49.80   $49.80  
  Purchase #5 $248.47   9.612%   $272.3529   $272.35   $272.35   $272.40  
  Purchase #6 $23.84   10.825%   $26.4207   $26.42   $26.40   $26.40  
  Purchase #7 $209.89   4.476%   $219.2847   $219.28   $219.30   $219.30  
  7 purchase totals = $1,024.24       $1,104.2558   $1,104.26   $1,104.30   $1,104.30