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 $216.41   11.837%   $242.0265   $242.03   $242.05   $242.00  
  Purchase #2 $232.33   13.739%   $264.2498   $264.25   $264.25   $264.20  
  Purchase #3 $182.92   6.360%   $194.5537   $194.55   $194.55   $194.60  
  Purchase #4 $107.65   13.588%   $122.2775   $122.28   $122.30   $122.30  
  Purchase #5 $244.50   6.217%   $259.7006   $259.70   $259.70   $259.70  
  Purchase #6 $87.45   4.449%   $91.3407   $91.34   $91.35   $91.30  
  Purchase #7 $153.28   5.755%   $162.1013   $162.10   $162.10   $162.10  
  7 purchase totals = $1,224.54       $1,336.2501   $1,336.25   $1,336.30   $1,336.20