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 $186.28   11.536%   $207.7693   $207.77   $207.75   $207.80  
  Purchase #2 $68.57   10.780%   $75.9618   $75.96   $75.95   $76.00  
  Purchase #3 $218.34   6.377%   $232.2635   $232.26   $232.25   $232.30  
  Purchase #4 $232.52   11.615%   $259.5272   $259.53   $259.55   $259.50  
  Purchase #5 $39.63   5.201%   $41.6912   $41.69   $41.70   $41.70  
  Purchase #6 $36.29   8.779%   $39.4759   $39.48   $39.50   $39.50  
  Purchase #7 $87.96   4.156%   $91.6156   $91.62   $91.60   $91.60  
  7 purchase totals = $869.59       $948.3045   $948.31   $948.30   $948.40