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 $234.85   13.715%   $267.0597   $267.06   $267.05   $267.10  
  Purchase #2 $238.54   13.107%   $269.8054   $269.81   $269.80   $269.80  
  Purchase #3 $109.55   9.497%   $119.954   $119.95   $119.95   $120.00  
  Purchase #4 $119.73   4.320%   $124.9023   $124.90   $124.90   $124.90  
  Purchase #5 $231.97   6.841%   $247.8391   $247.84   $247.85   $247.80  
  Purchase #6 $164.84   3.686%   $170.916   $170.92   $170.90   $170.90  
  Purchase #7 $8.52   13.376%   $9.6596   $9.66   $9.65   $9.70  
  7 purchase totals = $1,108.00       $1,210.1361   $1,210.14   $1,210.10   $1,210.20