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 $106.32   11.609%   $118.6627   $118.66   $118.65   $118.70  
  Purchase #2 $17.85   4.761%   $18.6998   $18.70   $18.70   $18.70  
  Purchase #3 $191.85   4.358%   $200.2108   $200.21   $200.20   $200.20  
  Purchase #4 $65.67   4.203%   $68.4301   $68.43   $68.45   $68.40  
  Purchase #5 $178.94   11.551%   $199.6094   $199.61   $199.60   $199.60  
  Purchase #6 $68.34   6.654%   $72.8873   $72.89   $72.90   $72.90  
  Purchase #7 $231.43   6.306%   $246.024   $246.02   $246.00   $246.00  
  7 purchase totals = $860.40       $924.5241   $924.52   $924.50   $924.50