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 $228.43   8.231%   $247.2321   $247.23   $247.25   $247.20  
  Purchase #2 $235.53   13.792%   $268.0143   $268.01   $268.00   $268.00  
  Purchase #3 $186.89   11.298%   $208.0048   $208.00   $208.00   $208.00  
  Purchase #4 $129.58   11.321%   $144.2498   $144.25   $144.25   $144.20  
  Purchase #5 $39.55   12.174%   $44.3648   $44.36   $44.35   $44.40  
  Purchase #6 $24.59   13.234%   $27.8442   $27.84   $27.85   $27.80  
  Purchase #7 $239.36   5.192%   $251.7876   $251.79   $251.80   $251.80  
  7 purchase totals = $1,083.93       $1,191.4976   $1,191.48   $1,191.50   $1,191.40