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 $205.55   3.307%   $212.3475   $212.35   $212.35   $212.30  
  Purchase #2 $77.74   11.342%   $86.5573   $86.56   $86.55   $86.60  
  Purchase #3 $214.60   6.590%   $228.7421   $228.74   $228.75   $228.70  
  Purchase #4 $190.64   10.139%   $209.969   $209.97   $209.95   $210.00  
  Purchase #5 $56.43   9.339%   $61.7   $61.70   $61.70   $61.70  
  Purchase #6 $218.73   12.494%   $246.0581   $246.06   $246.05   $246.10  
  Purchase #7 $232.44   4.122%   $242.0212   $242.02   $242.00   $242.00  
  7 purchase totals = $1,196.13       $1,287.3952   $1,287.40   $1,287.35   $1,287.40