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 $173.89   11.577%   $194.0212   $194.02   $194.00   $194.00  
  Purchase #2 $110.40   6.595%   $117.6809   $117.68   $117.70   $117.70  
  Purchase #3 $171.77   3.204%   $177.2735   $177.27   $177.25   $177.30  
  Purchase #4 $214.49   9.670%   $235.2312   $235.23   $235.25   $235.20  
  Purchase #5 $161.59   12.533%   $181.8421   $181.84   $181.85   $181.80  
  Purchase #6 $62.83   3.573%   $65.0749   $65.07   $65.05   $65.10  
  Purchase #7 $129.98   13.392%   $147.3869   $147.39   $147.40   $147.40  
  7 purchase totals = $1,024.95       $1,118.5107   $1,118.50   $1,118.50   $1,118.50