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 $111.55   10.792%   $123.5885   $123.59   $123.60   $123.60  
  Purchase #2 $184.87   13.151%   $209.1823   $209.18   $209.20   $209.20  
  Purchase #3 $119.52   9.308%   $130.6449   $130.64   $130.65   $130.60  
  Purchase #4 $127.48   5.274%   $134.2033   $134.20   $134.20   $134.20  
  Purchase #5 $234.35   4.346%   $244.5349   $244.53   $244.55   $244.50  
  Purchase #6 $211.99   9.756%   $232.6717   $232.67   $232.65   $232.70  
  Purchase #7 $132.26   3.182%   $136.4685   $136.47   $136.45   $136.50  
  7 purchase totals = $1,122.02       $1,211.2941   $1,211.28   $1,211.30   $1,211.30