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 $22.52   5.494%   $23.7572   $23.76   $23.75   $23.80  
  Purchase #2 $174.57   9.781%   $191.6447   $191.64   $191.65   $191.60  
  Purchase #3 $164.97   4.122%   $171.7701   $171.77   $171.75   $171.80  
  Purchase #4 $126.52   12.528%   $142.3704   $142.37   $142.35   $142.40  
  Purchase #5 $198.62   3.620%   $205.81   $205.81   $205.80   $205.80  
  Purchase #6 $217.66   3.462%   $225.1954   $225.20   $225.20   $225.20  
  Purchase #7 $126.88   13.293%   $143.7462   $143.75   $143.75   $143.70  
  7 purchase totals = $1,031.74       $1,104.2940   $1,104.30   $1,104.25   $1,104.30