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 $206.44   5.306%   $217.3937   $217.39   $217.40   $217.40  
  Purchase #2 $23.30   11.453%   $25.9685   $25.97   $25.95   $26.00  
  Purchase #3 $234.47   6.419%   $249.5206   $249.52   $249.50   $249.50  
  Purchase #4 $62.49   4.301%   $65.1777   $65.18   $65.20   $65.20  
  Purchase #5 $244.31   4.142%   $254.4293   $254.43   $254.45   $254.40  
  Purchase #6 $121.64   8.202%   $131.6169   $131.62   $131.60   $131.60  
  Purchase #7 $59.57   4.505%   $62.2536   $62.25   $62.25   $62.30  
  7 purchase totals = $952.22       $1,006.3603   $1,006.36   $1,006.35   $1,006.40