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 $246.48   13.476%   $279.6956   $279.70   $279.70   $279.70  
  Purchase #2 $121.86   3.187%   $125.7437   $125.74   $125.75   $125.70  
  Purchase #3 $140.44   9.284%   $153.4784   $153.48   $153.50   $153.50  
  Purchase #4 $18.47   9.776%   $20.2756   $20.28   $20.30   $20.30  
  Purchase #5 $247.82   6.178%   $263.1303   $263.13   $263.15   $263.10  
  Purchase #6 $163.41   10.371%   $180.3573   $180.36   $180.35   $180.40  
  Purchase #7 $209.69   13.270%   $237.5159   $237.52   $237.50   $237.50  
  7 purchase totals = $1,148.17       $1,260.1968   $1,260.21   $1,260.25   $1,260.20