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 $24.26   13.497%   $27.5344   $27.53   $27.55   $27.50  
  Purchase #2 $235.96   12.390%   $265.1954   $265.20   $265.20   $265.20  
  Purchase #3 $67.73   4.644%   $70.8754   $70.88   $70.90   $70.90  
  Purchase #4 $224.60   11.474%   $250.3706   $250.37   $250.35   $250.40  
  Purchase #5 $135.64   10.689%   $150.1386   $150.14   $150.15   $150.10  
  Purchase #6 $227.71   5.489%   $240.209   $240.21   $240.20   $240.20  
  Purchase #7 $45.84   9.731%   $50.3007   $50.30   $50.30   $50.30  
  7 purchase totals = $961.74       $1,054.6241   $1,054.63   $1,054.65   $1,054.60