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 $139.76   8.179%   $151.191   $151.19   $151.20   $151.20  
  Purchase #2 $239.80   11.176%   $266.6   $266.60   $266.60   $266.60  
  Purchase #3 $159.65   10.860%   $176.988   $176.99   $177.00   $177.00  
  Purchase #4 $88.45   4.364%   $92.31   $92.31   $92.30   $92.30  
  Purchase #5 $34.42   11.335%   $38.3215   $38.32   $38.30   $38.30  
  Purchase #6 $189.84   7.618%   $204.302   $204.30   $204.30   $204.30  
  Purchase #7 $202.45   10.514%   $223.7356   $223.74   $223.75   $223.70  
  7 purchase totals = $1,054.37       $1,153.4481   $1,153.45   $1,153.45   $1,153.40