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 $185.75   9.800%   $203.9535   $203.95   $203.95   $204.00  
  Purchase #2 $83.59   12.488%   $94.0287   $94.03   $94.05   $94.00  
  Purchase #3 $55.30   8.366%   $59.9264   $59.93   $59.95   $59.90  
  Purchase #4 $241.38   5.102%   $253.6952   $253.70   $253.70   $253.70  
  Purchase #5 $13.66   3.595%   $14.1511   $14.15   $14.15   $14.20  
  Purchase #6 $213.99   8.687%   $232.5793   $232.58   $232.60   $232.60  
  Purchase #7 $195.72   3.715%   $202.991   $202.99   $203.00   $203.00  
  7 purchase totals = $989.39       $1,061.3252   $1,061.33   $1,061.40   $1,061.40