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 $206.65   12.325%   $232.1196   $232.12   $232.10   $232.10  
  Purchase #2 $89.71   6.769%   $95.7825   $95.78   $95.80   $95.80  
  Purchase #3 $161.37   6.134%   $171.2684   $171.27   $171.25   $171.30  
  Purchase #4 $142.81   12.371%   $160.477   $160.48   $160.50   $160.50  
  Purchase #5 $190.84   12.217%   $214.1549   $214.15   $214.15   $214.20  
  Purchase #6 $162.90   9.284%   $178.0236   $178.02   $178.00   $178.00  
  Purchase #7 $99.91   7.396%   $107.2993   $107.30   $107.30   $107.30  
  7 purchase totals = $1,054.19       $1,159.1253   $1,159.12   $1,159.10   $1,159.20