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 $146.97   9.612%   $161.0968   $161.10   $161.10   $161.10  
  Purchase #2 $117.99   6.249%   $125.3632   $125.36   $125.35   $125.40  
  Purchase #3 $144.85   6.857%   $154.7824   $154.78   $154.80   $154.80  
  Purchase #4 $211.36   4.401%   $220.662   $220.66   $220.65   $220.70  
  Purchase #5 $142.66   10.290%   $157.3397   $157.34   $157.35   $157.30  
  Purchase #6 $239.92   11.411%   $267.2973   $267.30   $267.30   $267.30  
  Purchase #7 $154.53   11.654%   $172.5389   $172.54   $172.55   $172.50  
  7 purchase totals = $1,158.28       $1,259.0803   $1,259.08   $1,259.10   $1,259.10