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 $244.80   9.293%   $267.5493   $267.55   $267.55   $267.50  
  Purchase #2 $190.99   10.769%   $211.5577   $211.56   $211.55   $211.60  
  Purchase #3 $7.46   9.693%   $8.1831   $8.18   $8.20   $8.20  
  Purchase #4 $227.71   10.510%   $251.6423   $251.64   $251.65   $251.60  
  Purchase #5 $99.82   9.743%   $109.5455   $109.55   $109.55   $109.50  
  Purchase #6 $187.32   9.503%   $205.121   $205.12   $205.10   $205.10  
  Purchase #7 $6.75   4.780%   $7.0727   $7.07   $7.05   $7.10  
  7 purchase totals = $964.85       $1,060.6716   $1,060.67   $1,060.65   $1,060.60