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 $178.58   3.741%   $185.2607   $185.26   $185.25   $185.30  
  Purchase #2 $143.51   6.255%   $152.4866   $152.49   $152.50   $152.50  
  Purchase #3 $218.77   11.603%   $244.1539   $244.15   $244.15   $244.20  
  Purchase #4 $22.58   12.144%   $25.3221   $25.32   $25.30   $25.30  
  Purchase #5 $199.44   13.238%   $225.8419   $225.84   $225.85   $225.80  
  Purchase #6 $187.54   3.607%   $194.3046   $194.30   $194.30   $194.30  
  Purchase #7 $146.53   6.163%   $155.5606   $155.56   $155.55   $155.60  
  7 purchase totals = $1,096.95       $1,182.9304   $1,182.92   $1,182.90   $1,183.00