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 $142.41   3.844%   $147.8842   $147.88   $147.90   $147.90  
  Purchase #2 $222.91   3.366%   $230.4132   $230.41   $230.40   $230.40  
  Purchase #3 $250.58   7.656%   $269.7644   $269.76   $269.75   $269.80  
  Purchase #4 $209.91   13.238%   $237.6979   $237.70   $237.70   $237.70  
  Purchase #5 $134.39   4.806%   $140.8488   $140.85   $140.85   $140.80  
  Purchase #6 $201.38   8.756%   $219.0128   $219.01   $219.00   $219.00  
  Purchase #7 $66.52   8.516%   $72.1848   $72.18   $72.20   $72.20  
  7 purchase totals = $1,228.10       $1,317.8061   $1,317.79   $1,317.80   $1,317.80