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 $88.61   3.376%   $91.6015   $91.60   $91.60   $91.60  
  Purchase #2 $214.86   6.548%   $228.929   $228.93   $228.95   $228.90  
  Purchase #3 $247.86   6.558%   $264.1147   $264.11   $264.10   $264.10  
  Purchase #4 $232.35   9.295%   $253.9469   $253.95   $253.95   $253.90  
  Purchase #5 $83.35   5.102%   $87.6025   $87.60   $87.60   $87.60  
  Purchase #6 $197.70   7.868%   $213.255   $213.26   $213.25   $213.30  
  Purchase #7 $116.27   10.673%   $128.6795   $128.68   $128.70   $128.70  
  7 purchase totals = $1,181.00       $1,268.1291   $1,268.13   $1,268.15   $1,268.10