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 $151.67   9.780%   $166.5033   $166.50   $166.50   $166.50  
  Purchase #2 $243.72   5.302%   $256.642   $256.64   $256.65   $256.60  
  Purchase #3 $156.94   10.600%   $173.5756   $173.58   $173.60   $173.60  
  Purchase #4 $53.55   12.733%   $60.3685   $60.37   $60.35   $60.40  
  Purchase #5 $125.70   6.680%   $134.0968   $134.10   $134.10   $134.10  
  Purchase #6 $12.36   3.423%   $12.7831   $12.78   $12.80   $12.80  
  Purchase #7 $59.72   9.286%   $65.2656   $65.27   $65.25   $65.30  
  7 purchase totals = $803.66       $869.2349   $869.24   $869.25   $869.30