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 $30.87   11.663%   $34.4704   $34.47   $34.45   $34.50  
  Purchase #2 $246.39   7.727%   $265.4286   $265.43   $265.45   $265.40  
  Purchase #3 $192.52   9.750%   $211.2907   $211.29   $211.30   $211.30  
  Purchase #4 $243.74   3.730%   $252.8315   $252.83   $252.85   $252.80  
  Purchase #5 $86.29   3.374%   $89.2014   $89.20   $89.20   $89.20  
  Purchase #6 $182.26   10.807%   $201.9568   $201.96   $201.95   $202.00  
  Purchase #7 $143.69   6.263%   $152.6893   $152.69   $152.70   $152.70  
  7 purchase totals = $1,125.76       $1,207.8687   $1,207.87   $1,207.90   $1,207.90