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 $194.37   4.611%   $203.3324   $203.33   $203.35   $203.30  
  Purchase #2 $19.53   4.277%   $20.3653   $20.37   $20.35   $20.40  
  Purchase #3 $193.95   13.207%   $219.565   $219.57   $219.55   $219.60  
  Purchase #4 $181.45   8.420%   $196.7281   $196.73   $196.75   $196.70  
  Purchase #5 $214.78   13.769%   $244.3531   $244.35   $244.35   $244.40  
  Purchase #6 $245.72   9.491%   $269.0413   $269.04   $269.05   $269.00  
  Purchase #7 $95.62   6.212%   $101.5599   $101.56   $101.55   $101.60  
  7 purchase totals = $1,145.42       $1,254.9451   $1,254.95   $1,254.95   $1,255.00