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 $83.98   11.461%   $93.6049   $93.60   $93.60   $93.60  
  Purchase #2 $194.41   3.730%   $201.6615   $201.66   $201.65   $201.70  
  Purchase #3 $180.32   10.715%   $199.6413   $199.64   $199.65   $199.60  
  Purchase #4 $170.45   6.199%   $181.0162   $181.02   $181.00   $181.00  
  Purchase #5 $127.72   6.524%   $136.0525   $136.05   $136.05   $136.10  
  Purchase #6 $60.34   5.853%   $63.8717   $63.87   $63.85   $63.90  
  Purchase #7 $205.53   4.377%   $214.526   $214.53   $214.55   $214.50  
  7 purchase totals = $1,022.75       $1,090.3741   $1,090.37   $1,090.35   $1,090.40