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 $91.70   13.649%   $104.2161   $104.22   $104.20   $104.20  
  Purchase #2 $243.29   9.615%   $266.6823   $266.68   $266.70   $266.70  
  Purchase #3 $111.62   13.462%   $126.6463   $126.65   $126.65   $126.60  
  Purchase #4 $63.67   7.812%   $68.6439   $68.64   $68.65   $68.60  
  Purchase #5 $57.43   7.722%   $61.8647   $61.86   $61.85   $61.90  
  Purchase #6 $161.39   11.390%   $179.7723   $179.77   $179.75   $179.80  
  Purchase #7 $205.65   8.408%   $222.9411   $222.94   $222.95   $222.90  
  7 purchase totals = $934.75       $1,030.7667   $1,030.76   $1,030.75   $1,030.70