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 $233.96   12.458%   $263.1067   $263.11   $263.10   $263.10  
  Purchase #2 $145.37   13.342%   $164.7653   $164.77   $164.75   $164.80  
  Purchase #3 $49.62   7.362%   $53.273   $53.27   $53.25   $53.30  
  Purchase #4 $192.49   7.604%   $207.1269   $207.13   $207.15   $207.10  
  Purchase #5 $242.83   8.793%   $264.182   $264.18   $264.20   $264.20  
  Purchase #6 $168.62   12.291%   $189.3451   $189.35   $189.35   $189.30  
  Purchase #7 $41.89   8.254%   $45.3476   $45.35   $45.35   $45.30  
  7 purchase totals = $1,074.78       $1,187.1466   $1,187.16   $1,187.15   $1,187.10