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 $82.25   11.361%   $91.5944   $91.59   $91.60   $91.60  
  Purchase #2 $104.48   7.500%   $112.316   $112.32   $112.30   $112.30  
  Purchase #3 $79.64   4.240%   $83.0167   $83.02   $83.00   $83.00  
  Purchase #4 $24.80   4.690%   $25.9631   $25.96   $25.95   $26.00  
  Purchase #5 $170.31   13.262%   $192.8965   $192.90   $192.90   $192.90  
  Purchase #6 $226.86   6.444%   $241.4789   $241.48   $241.50   $241.50  
  Purchase #7 $23.64   8.350%   $25.6139   $25.61   $25.60   $25.60  
  7 purchase totals = $711.98       $772.8795   $772.88   $772.85   $772.90