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 $209.95   11.599%   $234.3021   $234.30   $234.30   $234.30  
  Purchase #2 $121.81   11.111%   $135.3443   $135.34   $135.35   $135.30  
  Purchase #3 $135.98   8.372%   $147.3642   $147.36   $147.35   $147.40  
  Purchase #4 $168.50   4.791%   $176.5728   $176.57   $176.55   $176.60  
  Purchase #5 $228.68   7.512%   $245.8584   $245.86   $245.85   $245.90  
  Purchase #6 $214.29   5.150%   $225.3259   $225.33   $225.35   $225.30  
  Purchase #7 $87.77   11.185%   $97.5871   $97.59   $97.60   $97.60  
  7 purchase totals = $1,166.98       $1,262.3548   $1,262.35   $1,262.35   $1,262.40