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 $91.82   4.127%   $95.6094   $95.61   $95.60   $95.60  
  Purchase #2 $111.25   11.315%   $123.8379   $123.84   $123.85   $123.80  
  Purchase #3 $237.91   9.276%   $259.9785   $259.98   $260.00   $260.00  
  Purchase #4 $238.75   10.633%   $264.1363   $264.14   $264.15   $264.10  
  Purchase #5 $205.49   10.312%   $226.6801   $226.68   $226.70   $226.70  
  Purchase #6 $75.44   6.534%   $80.3692   $80.37   $80.35   $80.40  
  Purchase #7 $20.58   12.693%   $23.1922   $23.19   $23.20   $23.20  
  7 purchase totals = $981.24       $1,073.8036   $1,073.81   $1,073.85   $1,073.80