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 $194.79   12.720%   $219.5673   $219.57   $219.55   $219.60  
  Purchase #2 $24.56   5.872%   $26.0022   $26.00   $26.00   $26.00  
  Purchase #3 $191.53   6.613%   $204.1959   $204.20   $204.20   $204.20  
  Purchase #4 $203.69   4.667%   $213.1962   $213.20   $213.20   $213.20  
  Purchase #5 $112.38   9.796%   $123.3887   $123.39   $123.40   $123.40  
  Purchase #6 $132.82   7.186%   $142.3644   $142.36   $142.35   $142.40  
  Purchase #7 $108.55   9.159%   $118.4921   $118.49   $118.50   $118.50  
  7 purchase totals = $968.32       $1,047.2068   $1,047.21   $1,047.20   $1,047.30