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 $76.89   13.446%   $87.2286   $87.23   $87.25   $87.20  
  Purchase #2 $228.58   6.374%   $243.1497   $243.15   $243.15   $243.10  
  Purchase #3 $108.40   11.789%   $121.1793   $121.18   $121.20   $121.20  
  Purchase #4 $26.99   6.143%   $28.648   $28.65   $28.65   $28.60  
  Purchase #5 $83.26   4.268%   $86.8135   $86.81   $86.80   $86.80  
  Purchase #6 $225.49   11.788%   $252.0708   $252.07   $252.05   $252.10  
  Purchase #7 $226.84   4.863%   $237.8712   $237.87   $237.85   $237.90  
  7 purchase totals = $976.45       $1,056.9611   $1,056.96   $1,056.95   $1,056.90