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 $235.47   7.673%   $253.5376   $253.54   $253.55   $253.50  
  Purchase #2 $107.25   5.790%   $113.4598   $113.46   $113.45   $113.50  
  Purchase #3 $106.31   10.348%   $117.311   $117.31   $117.30   $117.30  
  Purchase #4 $23.68   9.692%   $25.9751   $25.98   $26.00   $26.00  
  Purchase #5 $175.80   5.759%   $185.9243   $185.92   $185.90   $185.90  
  Purchase #6 $205.26   3.386%   $212.2101   $212.21   $212.20   $212.20  
  Purchase #7 $98.51   12.865%   $111.1833   $111.18   $111.20   $111.20  
  7 purchase totals = $952.28       $1,019.6012   $1,019.60   $1,019.60   $1,019.60