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 $134.85   8.652%   $146.5172   $146.52   $146.50   $146.50  
  Purchase #2 $208.37   6.322%   $221.5432   $221.54   $221.55   $221.50  
  Purchase #3 $110.94   12.506%   $124.8142   $124.81   $124.80   $124.80  
  Purchase #4 $231.77   13.604%   $263.3   $263.30   $263.30   $263.30  
  Purchase #5 $102.35   3.569%   $106.0029   $106.00   $106.00   $106.00  
  Purchase #6 $64.89   3.586%   $67.217   $67.22   $67.20   $67.20  
  Purchase #7 $225.91   12.128%   $253.3084   $253.31   $253.30   $253.30  
  7 purchase totals = $1,079.08       $1,182.7029   $1,182.70   $1,182.65   $1,182.60