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 $183.74   12.217%   $206.1875   $206.19   $206.20   $206.20  
  Purchase #2 $125.89   7.753%   $135.6503   $135.65   $135.65   $135.70  
  Purchase #3 $88.54   6.562%   $94.35   $94.35   $94.35   $94.40  
  Purchase #4 $227.93   3.486%   $235.8756   $235.88   $235.90   $235.90  
  Purchase #5 $215.70   8.599%   $234.248   $234.25   $234.25   $234.20  
  Purchase #6 $45.56   5.536%   $48.0822   $48.08   $48.10   $48.10  
  Purchase #7 $218.63   8.658%   $237.559   $237.56   $237.55   $237.60  
  7 purchase totals = $1,105.99       $1,191.9526   $1,191.96   $1,192.00   $1,192.10