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 $175.35   10.536%   $193.8249   $193.82   $193.80   $193.80  
  Purchase #2 $165.94   5.426%   $174.9439   $174.94   $174.95   $174.90  
  Purchase #3 $247.67   3.336%   $255.9323   $255.93   $255.95   $255.90  
  Purchase #4 $23.74   7.616%   $25.548   $25.55   $25.55   $25.50  
  Purchase #5 $164.43   10.208%   $181.215   $181.22   $181.20   $181.20  
  Purchase #6 $230.78   10.409%   $254.8019   $254.80   $254.80   $254.80  
  Purchase #7 $95.90   8.596%   $104.1436   $104.14   $104.15   $104.10  
  7 purchase totals = $1,103.81       $1,190.4096   $1,190.40   $1,190.40   $1,190.20