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 $66.65   3.398%   $68.9148   $68.91   $68.90   $68.90  
  Purchase #2 $191.68   8.342%   $207.6699   $207.67   $207.65   $207.70  
  Purchase #3 $214.48   3.335%   $221.6329   $221.63   $221.65   $221.60  
  Purchase #4 $41.94   12.321%   $47.1074   $47.11   $47.10   $47.10  
  Purchase #5 $241.31   7.337%   $259.0149   $259.01   $259.00   $259.00  
  Purchase #6 $61.25   9.220%   $66.8973   $66.90   $66.90   $66.90  
  Purchase #7 $181.95   12.173%   $204.0988   $204.10   $204.10   $204.10  
  7 purchase totals = $999.26       $1,075.3360   $1,075.33   $1,075.30   $1,075.30