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 $198.38   4.779%   $207.8606   $207.86   $207.85   $207.90  
  Purchase #2 $23.82   10.121%   $26.2308   $26.23   $26.25   $26.20  
  Purchase #3 $141.51   8.174%   $153.077   $153.08   $153.10   $153.10  
  Purchase #4 $203.83   5.745%   $215.54   $215.54   $215.55   $215.50  
  Purchase #5 $141.41   5.547%   $149.254   $149.25   $149.25   $149.30  
  Purchase #6 $239.29   12.236%   $268.5695   $268.57   $268.55   $268.60  
  Purchase #7 $172.92   9.816%   $189.8938   $189.89   $189.90   $189.90  
  7 purchase totals = $1,121.16       $1,210.4257   $1,210.42   $1,210.45   $1,210.50