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 $192.26   9.833%   $211.1649   $211.16   $211.15   $211.20  
  Purchase #2 $54.93   5.775%   $58.1022   $58.10   $58.10   $58.10  
  Purchase #3 $6.26   9.581%   $6.8598   $6.86   $6.85   $6.90  
  Purchase #4 $92.31   5.704%   $97.5754   $97.58   $97.60   $97.60  
  Purchase #5 $105.92   4.168%   $110.3347   $110.33   $110.35   $110.30  
  Purchase #6 $152.74   11.647%   $170.5296   $170.53   $170.55   $170.50  
  Purchase #7 $86.35   10.446%   $95.3701   $95.37   $95.35   $95.40  
  7 purchase totals = $690.77       $749.9367   $749.93   $749.95   $750.00