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 $88.60   10.775%   $98.1467   $98.15   $98.15   $98.10  
  Purchase #2 $215.79   8.580%   $234.3048   $234.30   $234.30   $234.30  
  Purchase #3 $127.37   4.445%   $133.0316   $133.03   $133.05   $133.00  
  Purchase #4 $45.57   8.827%   $49.5925   $49.59   $49.60   $49.60  
  Purchase #5 $118.56   6.652%   $126.4466   $126.45   $126.45   $126.40  
  Purchase #6 $231.74   3.792%   $240.5276   $240.53   $240.55   $240.50  
  Purchase #7 $168.53   12.566%   $189.7075   $189.71   $189.70   $189.70  
  7 purchase totals = $996.16       $1,071.7573   $1,071.76   $1,071.80   $1,071.60