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 $180.56   11.851%   $201.9582   $201.96   $201.95   $202.00  
  Purchase #2 $148.54   4.469%   $155.1783   $155.18   $155.20   $155.20  
  Purchase #3 $209.45   11.556%   $233.654   $233.65   $233.65   $233.70  
  Purchase #4 $54.32   13.750%   $61.789   $61.79   $61.80   $61.80  
  Purchase #5 $20.25   11.564%   $22.5917   $22.59   $22.60   $22.60  
  Purchase #6 $185.49   6.473%   $197.4968   $197.50   $197.50   $197.50  
  Purchase #7 $122.30   13.257%   $138.5133   $138.51   $138.50   $138.50  
  7 purchase totals = $920.91       $1,011.1813   $1,011.18   $1,011.20   $1,011.30