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 $165.41   13.217%   $187.2722   $187.27   $187.25   $187.30  
  Purchase #2 $186.73   3.816%   $193.8556   $193.86   $193.85   $193.90  
  Purchase #3 $228.54   10.573%   $252.7035   $252.70   $252.70   $252.70  
  Purchase #4 $205.37   9.829%   $225.5558   $225.56   $225.55   $225.60  
  Purchase #5 $22.34   7.647%   $24.0483   $24.05   $24.05   $24.00  
  Purchase #6 $119.74   12.593%   $134.8189   $134.82   $134.80   $134.80  
  Purchase #7 $73.89   6.501%   $78.6936   $78.69   $78.70   $78.70  
  7 purchase totals = $1,002.02       $1,096.9479   $1,096.95   $1,096.90   $1,097.00