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 $125.49   6.802%   $134.0258   $134.03   $134.05   $134.00  
  Purchase #2 $8.42   11.347%   $9.3754   $9.38   $9.40   $9.40  
  Purchase #3 $102.59   6.872%   $109.64   $109.64   $109.65   $109.60  
  Purchase #4 $161.77   6.528%   $172.3303   $172.33   $172.35   $172.30  
  Purchase #5 $183.39   3.783%   $190.3276   $190.33   $190.35   $190.30  
  Purchase #6 $113.36   10.569%   $125.341   $125.34   $125.35   $125.30  
  Purchase #7 $61.58   7.123%   $65.9663   $65.97   $65.95   $66.00  
  7 purchase totals = $756.60       $807.0064   $807.02   $807.10   $806.90