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 $153.58   9.772%   $168.5878   $168.59   $168.60   $168.60  
  Purchase #2 $188.88   4.386%   $197.1643   $197.16   $197.15   $197.20  
  Purchase #3 $74.53   6.158%   $79.1196   $79.12   $79.10   $79.10  
  Purchase #4 $218.64   7.459%   $234.9484   $234.95   $234.95   $234.90  
  Purchase #5 $197.31   10.283%   $217.5994   $217.60   $217.60   $217.60  
  Purchase #6 $29.91   9.220%   $32.6677   $32.67   $32.65   $32.70  
  Purchase #7 $244.90   7.787%   $263.9704   $263.97   $263.95   $264.00  
  7 purchase totals = $1,107.75       $1,194.0576   $1,194.06   $1,194.00   $1,194.10