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 $176.47   12.771%   $199.007   $199.01   $199.00   $199.00  
  Purchase #2 $122.59   4.262%   $127.8148   $127.81   $127.80   $127.80  
  Purchase #3 $60.28   4.648%   $63.0818   $63.08   $63.10   $63.10  
  Purchase #4 $80.60   5.697%   $85.1918   $85.19   $85.20   $85.20  
  Purchase #5 $151.48   8.644%   $164.5739   $164.57   $164.55   $164.60  
  Purchase #6 $68.76   6.774%   $73.4178   $73.42   $73.40   $73.40  
  Purchase #7 $244.52   9.249%   $267.1357   $267.14   $267.15   $267.10  
  7 purchase totals = $904.70       $980.2228   $980.22   $980.20   $980.20