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 $160.90   4.354%   $167.9056   $167.91   $167.90   $167.90  
  Purchase #2 $158.97   9.676%   $174.3519   $174.35   $174.35   $174.40  
  Purchase #3 $225.47   7.293%   $241.9135   $241.91   $241.90   $241.90  
  Purchase #4 $187.75   9.184%   $204.993   $204.99   $205.00   $205.00  
  Purchase #5 $53.41   11.711%   $59.6648   $59.66   $59.65   $59.70  
  Purchase #6 $235.84   11.489%   $262.9357   $262.94   $262.95   $262.90  
  Purchase #7 $142.31   3.120%   $146.7501   $146.75   $146.75   $146.80  
  7 purchase totals = $1,164.65       $1,258.5146   $1,258.51   $1,258.50   $1,258.60