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 $196.61   11.730%   $219.6724   $219.67   $219.65   $219.70  
  Purchase #2 $250.92   8.477%   $272.1905   $272.19   $272.20   $272.20  
  Purchase #3 $19.37   4.849%   $20.3093   $20.31   $20.30   $20.30  
  Purchase #4 $121.52   10.616%   $134.4206   $134.42   $134.40   $134.40  
  Purchase #5 $175.37   6.395%   $186.5849   $186.58   $186.60   $186.60  
  Purchase #6 $118.84   11.254%   $132.2143   $132.21   $132.20   $132.20  
  Purchase #7 $163.61   13.518%   $185.7268   $185.73   $185.75   $185.70  
  7 purchase totals = $1,046.24       $1,151.1188   $1,151.11   $1,151.10   $1,151.10