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 $78.95   5.830%   $83.5528   $83.55   $83.55   $83.60  
  Purchase #2 $11.44   7.535%   $12.302   $12.30   $12.30   $12.30  
  Purchase #3 $168.46   12.868%   $190.1374   $190.14   $190.15   $190.10  
  Purchase #4 $208.61   9.652%   $228.745   $228.75   $228.75   $228.70  
  Purchase #5 $55.72   7.521%   $59.9107   $59.91   $59.90   $59.90  
  Purchase #6 $239.94   11.362%   $267.202   $267.20   $267.20   $267.20  
  Purchase #7 $233.96   5.392%   $246.5751   $246.58   $246.60   $246.60  
  7 purchase totals = $997.08       $1,088.4250   $1,088.43   $1,088.45   $1,088.40