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 $52.83   9.659%   $57.9328   $57.93   $57.95   $57.90  
  Purchase #2 $6.59   5.741%   $6.9683   $6.97   $6.95   $7.00  
  Purchase #3 $66.62   5.731%   $70.438   $70.44   $70.45   $70.40  
  Purchase #4 $106.99   3.229%   $110.4447   $110.44   $110.45   $110.40  
  Purchase #5 $226.84   8.167%   $245.366   $245.37   $245.35   $245.40  
  Purchase #6 $56.64   11.868%   $63.362   $63.36   $63.35   $63.40  
  Purchase #7 $203.27   7.343%   $218.1961   $218.20   $218.20   $218.20  
  7 purchase totals = $719.78       $772.7079   $772.71   $772.70   $772.70