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 $87.64   10.660%   $96.9824   $96.98   $97.00   $97.00  
  Purchase #2 $121.29   7.268%   $130.1054   $130.11   $130.10   $130.10  
  Purchase #3 $24.70   6.172%   $26.2245   $26.22   $26.20   $26.20  
  Purchase #4 $34.46   6.280%   $36.6241   $36.62   $36.60   $36.60  
  Purchase #5 $221.40   4.526%   $231.4206   $231.42   $231.40   $231.40  
  Purchase #6 $206.84   10.645%   $228.8581   $228.86   $228.85   $228.90  
  Purchase #7 $239.56   9.722%   $262.85   $262.85   $262.85   $262.90  
  7 purchase totals = $935.89       $1,013.0651   $1,013.06   $1,013.00   $1,013.10