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 $224.41   4.619%   $234.7755   $234.78   $234.80   $234.80  
  Purchase #2 $243.40   9.526%   $266.5863   $266.59   $266.60   $266.60  
  Purchase #3 $82.80   7.633%   $89.1201   $89.12   $89.10   $89.10  
  Purchase #4 $170.30   9.608%   $186.6624   $186.66   $186.65   $186.70  
  Purchase #5 $150.77   11.177%   $167.6216   $167.62   $167.60   $167.60  
  Purchase #6 $198.45   3.132%   $204.6655   $204.67   $204.65   $204.70  
  Purchase #7 $91.45   13.789%   $104.06   $104.06   $104.05   $104.10  
  7 purchase totals = $1,161.58       $1,253.4914   $1,253.50   $1,253.45   $1,253.60