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 $113.98   9.469%   $124.7728   $124.77   $124.75   $124.80  
  Purchase #2 $186.29   3.189%   $192.2308   $192.23   $192.25   $192.20  
  Purchase #3 $74.29   11.747%   $83.0168   $83.02   $83.00   $83.00  
  Purchase #4 $192.83   9.477%   $211.1045   $211.10   $211.10   $211.10  
  Purchase #5 $162.41   13.344%   $184.082   $184.08   $184.10   $184.10  
  Purchase #6 $129.98   4.115%   $135.3287   $135.33   $135.35   $135.30  
  Purchase #7 $170.54   3.264%   $176.1064   $176.11   $176.10   $176.10  
  7 purchase totals = $1,030.32       $1,106.6420   $1,106.64   $1,106.65   $1,106.60