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 $226.35   11.771%   $252.9937   $252.99   $253.00   $253.00  
  Purchase #2 $173.59   4.832%   $181.9779   $181.98   $182.00   $182.00  
  Purchase #3 $124.56   11.368%   $138.72   $138.72   $138.70   $138.70  
  Purchase #4 $156.62   11.181%   $174.1317   $174.13   $174.15   $174.10  
  Purchase #5 $166.55   11.849%   $186.2845   $186.28   $186.30   $186.30  
  Purchase #6 $149.56   8.785%   $162.6988   $162.70   $162.70   $162.70  
  Purchase #7 $67.84   5.791%   $71.7686   $71.77   $71.75   $71.80  
  7 purchase totals = $1,065.07       $1,168.5752   $1,168.57   $1,168.60   $1,168.60