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 $244.68   9.503%   $267.9319   $267.93   $267.95   $267.90  
  Purchase #2 $246.67   7.245%   $264.5412   $264.54   $264.55   $264.50  
  Purchase #3 $6.91   10.361%   $7.6259   $7.63   $7.65   $7.60  
  Purchase #4 $199.88   9.545%   $218.9585   $218.96   $218.95   $219.00  
  Purchase #5 $155.25   6.155%   $164.8056   $164.81   $164.80   $164.80  
  Purchase #6 $217.34   5.780%   $229.9023   $229.90   $229.90   $229.90  
  Purchase #7 $158.75   4.290%   $165.5604   $165.56   $165.55   $165.60  
  7 purchase totals = $1,229.48       $1,319.3258   $1,319.33   $1,319.35   $1,319.30