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 $54.26   6.310%   $57.6838   $57.68   $57.70   $57.70  
  Purchase #2 $239.88   11.400%   $267.2263   $267.23   $267.25   $267.20  
  Purchase #3 $241.97   12.124%   $271.3064   $271.31   $271.30   $271.30  
  Purchase #4 $186.66   3.524%   $193.2379   $193.24   $193.25   $193.20  
  Purchase #5 $161.87   6.853%   $172.963   $172.96   $172.95   $173.00  
  Purchase #6 $6.70   11.872%   $7.4954   $7.50   $7.50   $7.50  
  Purchase #7 $136.26   6.254%   $144.7817   $144.78   $144.80   $144.80  
  7 purchase totals = $1,027.60       $1,114.6945   $1,114.70   $1,114.75   $1,114.70