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 $228.61   5.705%   $241.6522   $241.65   $241.65   $241.70  
  Purchase #2 $112.66   8.399%   $122.1223   $122.12   $122.10   $122.10  
  Purchase #3 $144.33   3.800%   $149.8145   $149.81   $149.80   $149.80  
  Purchase #4 $96.33   12.537%   $108.4069   $108.41   $108.40   $108.40  
  Purchase #5 $114.79   8.753%   $124.8376   $124.84   $124.85   $124.80  
  Purchase #6 $194.82   3.646%   $201.9231   $201.92   $201.90   $201.90  
  Purchase #7 $13.68   6.292%   $14.5407   $14.54   $14.55   $14.50  
  7 purchase totals = $905.22       $963.2973   $963.29   $963.25   $963.20