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 $186.70   10.855%   $206.9663   $206.97   $206.95   $207.00  
  Purchase #2 $8.93   12.727%   $10.0665   $10.07   $10.05   $10.10  
  Purchase #3 $241.29   3.829%   $250.529   $250.53   $250.55   $250.50  
  Purchase #4 $239.57   12.791%   $270.2134   $270.21   $270.20   $270.20  
  Purchase #5 $120.26   5.854%   $127.3   $127.30   $127.30   $127.30  
  Purchase #6 $180.49   3.344%   $186.5256   $186.53   $186.55   $186.50  
  Purchase #7 $247.75   10.792%   $274.4872   $274.49   $274.50   $274.50  
  7 purchase totals = $1,224.99       $1,326.0880   $1,326.10   $1,326.10   $1,326.10