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 $92.76   5.180%   $97.565   $97.57   $97.55   $97.60  
  Purchase #2 $179.37   9.654%   $196.6864   $196.69   $196.70   $196.70  
  Purchase #3 $45.43   6.851%   $48.5424   $48.54   $48.55   $48.50  
  Purchase #4 $154.42   12.652%   $173.9572   $173.96   $173.95   $174.00  
  Purchase #5 $217.70   3.642%   $225.6286   $225.63   $225.65   $225.60  
  Purchase #6 $198.29   12.462%   $223.0009   $223.00   $223.00   $223.00  
  Purchase #7 $24.98   3.330%   $25.8118   $25.81   $25.80   $25.80  
  7 purchase totals = $912.95       $991.1923   $991.20   $991.20   $991.20