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 $51.46   3.651%   $53.3388   $53.34   $53.35   $53.30  
  Purchase #2 $197.99   11.552%   $220.8618   $220.86   $220.85   $220.90  
  Purchase #3 $222.53   11.586%   $248.3123   $248.31   $248.30   $248.30  
  Purchase #4 $95.53   12.210%   $107.1942   $107.19   $107.20   $107.20  
  Purchase #5 $250.62   3.599%   $259.6398   $259.64   $259.65   $259.60  
  Purchase #6 $146.37   4.519%   $152.9845   $152.98   $153.00   $153.00  
  Purchase #7 $209.57   5.771%   $221.6643   $221.66   $221.65   $221.70  
  7 purchase totals = $1,174.07       $1,263.9957   $1,263.98   $1,264.00   $1,264.00