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 $118.36   8.104%   $127.9519   $127.95   $127.95   $128.00  
  Purchase #2 $6.25   9.372%   $6.8358   $6.84   $6.85   $6.80  
  Purchase #3 $102.41   13.158%   $115.8851   $115.89   $115.90   $115.90  
  Purchase #4 $106.32   11.304%   $118.3384   $118.34   $118.35   $118.30  
  Purchase #5 $246.98   6.243%   $262.399   $262.40   $262.40   $262.40  
  Purchase #6 $190.54   7.571%   $204.9658   $204.97   $204.95   $205.00  
  Purchase #7 $120.48   8.445%   $130.6545   $130.65   $130.65   $130.70  
  7 purchase totals = $891.34       $967.0305   $967.04   $967.05   $967.10