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 $77.59   11.779%   $86.7293   $86.73   $86.75   $86.70  
  Purchase #2 $141.80   8.850%   $154.3493   $154.35   $154.35   $154.30  
  Purchase #3 $221.87   10.432%   $245.0155   $245.02   $245.00   $245.00  
  Purchase #4 $224.52   6.461%   $239.0262   $239.03   $239.05   $239.00  
  Purchase #5 $63.84   12.478%   $71.806   $71.81   $71.80   $71.80  
  Purchase #6 $201.84   6.140%   $214.233   $214.23   $214.25   $214.20  
  Purchase #7 $7.96   10.742%   $8.8151   $8.82   $8.80   $8.80  
  7 purchase totals = $939.42       $1,019.9744   $1,019.99   $1,020.00   $1,019.80