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 $87.63   6.580%   $93.3961   $93.40   $93.40   $93.40  
  Purchase #2 $182.50   7.480%   $196.151   $196.15   $196.15   $196.20  
  Purchase #3 $165.87   6.691%   $176.9684   $176.97   $176.95   $177.00  
  Purchase #4 $167.29   4.284%   $174.4567   $174.46   $174.45   $174.50  
  Purchase #5 $244.87   13.500%   $277.9275   $277.93   $277.95   $277.90  
  Purchase #6 $244.73   6.419%   $260.4392   $260.44   $260.45   $260.40  
  Purchase #7 $151.72   13.561%   $172.2947   $172.29   $172.30   $172.30  
  7 purchase totals = $1,244.61       $1,351.6336   $1,351.64   $1,351.65   $1,351.70