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 $138.56   6.197%   $147.1466   $147.15   $147.15   $147.10  
  Purchase #2 $224.76   8.376%   $243.5859   $243.59   $243.60   $243.60  
  Purchase #3 $60.77   12.346%   $68.2727   $68.27   $68.25   $68.30  
  Purchase #4 $217.61   11.140%   $241.8518   $241.85   $241.85   $241.90  
  Purchase #5 $92.50   4.797%   $96.9372   $96.94   $96.95   $96.90  
  Purchase #6 $73.86   3.588%   $76.5101   $76.51   $76.50   $76.50  
  Purchase #7 $38.79   4.606%   $40.5767   $40.58   $40.60   $40.60  
  7 purchase totals = $846.85       $914.8810   $914.89   $914.90   $914.90