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 $54.58   11.808%   $61.0248   $61.02   $61.00   $61.00  
  Purchase #2 $198.31   4.506%   $207.2458   $207.25   $207.25   $207.20  
  Purchase #3 $170.57   10.822%   $189.0291   $189.03   $189.05   $189.00  
  Purchase #4 $27.64   7.562%   $29.7301   $29.73   $29.75   $29.70  
  Purchase #5 $245.29   8.149%   $265.2787   $265.28   $265.30   $265.30  
  Purchase #6 $204.65   13.617%   $232.5172   $232.52   $232.50   $232.50  
  Purchase #7 $81.85   5.687%   $86.5048   $86.50   $86.50   $86.50  
  7 purchase totals = $982.89       $1,071.3305   $1,071.33   $1,071.35   $1,071.20