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 $84.75   13.194%   $95.9319   $95.93   $95.95   $95.90  
  Purchase #2 $79.41   7.474%   $85.3451   $85.35   $85.35   $85.30  
  Purchase #3 $7.42   3.213%   $7.6584   $7.66   $7.65   $7.70  
  Purchase #4 $203.63   13.423%   $230.9633   $230.96   $230.95   $231.00  
  Purchase #5 $115.76   13.751%   $131.6782   $131.68   $131.70   $131.70  
  Purchase #6 $189.91   8.354%   $205.7751   $205.78   $205.80   $205.80  
  Purchase #7 $144.81   8.799%   $157.5518   $157.55   $157.55   $157.60  
  7 purchase totals = $825.69       $914.9038   $914.91   $914.95   $915.00