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 $231.68   4.750%   $242.6848   $242.68   $242.70   $242.70  
  Purchase #2 $241.87   5.363%   $254.8415   $254.84   $254.85   $254.80  
  Purchase #3 $51.97   11.549%   $57.972   $57.97   $57.95   $58.00  
  Purchase #4 $120.87   11.197%   $134.4038   $134.40   $134.40   $134.40  
  Purchase #5 $165.94   12.155%   $186.11   $186.11   $186.10   $186.10  
  Purchase #6 $217.52   5.490%   $229.4618   $229.46   $229.45   $229.50  
  Purchase #7 $77.40   13.242%   $87.6493   $87.65   $87.65   $87.60  
  7 purchase totals = $1,107.25       $1,193.1232   $1,193.11   $1,193.10   $1,193.10