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 $233.77   10.178%   $257.5631   $257.56   $257.55   $257.60  
  Purchase #2 $214.31   3.258%   $221.2922   $221.29   $221.30   $221.30  
  Purchase #3 $240.44   9.211%   $262.5869   $262.59   $262.60   $262.60  
  Purchase #4 $248.98   5.307%   $262.1934   $262.19   $262.20   $262.20  
  Purchase #5 $207.95   5.624%   $219.6451   $219.65   $219.65   $219.60  
  Purchase #6 $215.55   5.776%   $228.0002   $228.00   $228.00   $228.00  
  Purchase #7 $104.53   5.741%   $110.5311   $110.53   $110.55   $110.50  
  7 purchase totals = $1,465.53       $1,561.8120   $1,561.81   $1,561.85   $1,561.80