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 $64.85   6.431%   $69.0205   $69.02   $69.00   $69.00  
  Purchase #2 $233.68   11.605%   $260.7986   $260.80   $260.80   $260.80  
  Purchase #3 $104.73   11.658%   $116.9394   $116.94   $116.95   $116.90  
  Purchase #4 $124.80   3.291%   $128.9072   $128.91   $128.90   $128.90  
  Purchase #5 $45.65   4.493%   $47.7011   $47.70   $47.70   $47.70  
  Purchase #6 $212.38   6.172%   $225.4881   $225.49   $225.50   $225.50  
  Purchase #7 $194.41   6.766%   $207.5638   $207.56   $207.55   $207.60  
  7 purchase totals = $980.50       $1,056.4187   $1,056.42   $1,056.40   $1,056.40