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 $190.77   7.452%   $204.9862   $204.99   $205.00   $205.00  
  Purchase #2 $235.60   10.379%   $260.0529   $260.05   $260.05   $260.10  
  Purchase #3 $26.62   5.541%   $28.095   $28.10   $28.10   $28.10  
  Purchase #4 $84.92   5.293%   $89.4148   $89.41   $89.40   $89.40  
  Purchase #5 $204.50   10.526%   $226.0257   $226.03   $226.05   $226.00  
  Purchase #6 $58.77   6.123%   $62.3685   $62.37   $62.35   $62.40  
  Purchase #7 $186.34   4.280%   $194.3154   $194.32   $194.30   $194.30  
  7 purchase totals = $987.52       $1,065.2585   $1,065.27   $1,065.25   $1,065.30