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 $34.93   5.736%   $36.9336   $36.93   $36.95   $36.90  
  Purchase #2 $235.67   4.388%   $246.0112   $246.01   $246.00   $246.00  
  Purchase #3 $208.50   12.333%   $234.2143   $234.21   $234.20   $234.20  
  Purchase #4 $197.48   9.488%   $216.2169   $216.22   $216.20   $216.20  
  Purchase #5 $234.57   9.352%   $256.507   $256.51   $256.50   $256.50  
  Purchase #6 $212.83   6.209%   $226.0446   $226.04   $226.05   $226.00  
  Purchase #7 $221.51   11.212%   $246.3457   $246.35   $246.35   $246.30  
  7 purchase totals = $1,345.49       $1,462.2733   $1,462.27   $1,462.25   $1,462.10