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 $64.95   6.555%   $69.2075   $69.21   $69.20   $69.20  
  Purchase #2 $210.47   12.516%   $236.8124   $236.81   $236.80   $236.80  
  Purchase #3 $69.48   4.196%   $72.3954   $72.40   $72.40   $72.40  
  Purchase #4 $41.49   10.341%   $45.7805   $45.78   $45.80   $45.80  
  Purchase #5 $75.26   13.835%   $85.6722   $85.67   $85.65   $85.70  
  Purchase #6 $196.78   13.732%   $223.8018   $223.80   $223.80   $223.80  
  Purchase #7 $174.84   10.537%   $193.2629   $193.26   $193.25   $193.30  
  7 purchase totals = $833.27       $926.9327   $926.93   $926.90   $927.00