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 $199.56   5.611%   $210.7573   $210.76   $210.75   $210.80  
  Purchase #2 $32.85   5.545%   $34.6715   $34.67   $34.65   $34.70  
  Purchase #3 $232.41   3.777%   $241.1881   $241.19   $241.20   $241.20  
  Purchase #4 $230.49   8.698%   $250.538   $250.54   $250.55   $250.50  
  Purchase #5 $62.76   4.370%   $65.5026   $65.50   $65.50   $65.50  
  Purchase #6 $61.79   4.251%   $64.4167   $64.42   $64.40   $64.40  
  Purchase #7 $121.25   11.221%   $134.8555   $134.86   $134.85   $134.90  
  7 purchase totals = $941.11       $1,001.9297   $1,001.94   $1,001.90   $1,002.00