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 $217.78   3.307%   $224.982   $224.98   $225.00   $225.00  
  Purchase #2 $32.94   3.223%   $34.0017   $34.00   $34.00   $34.00  
  Purchase #3 $5.46   7.596%   $5.8747   $5.87   $5.85   $5.90  
  Purchase #4 $41.76   6.851%   $44.621   $44.62   $44.60   $44.60  
  Purchase #5 $234.33   5.273%   $246.6862   $246.69   $246.70   $246.70  
  Purchase #6 $45.49   9.107%   $49.6328   $49.63   $49.65   $49.60  
  Purchase #7 $168.55   9.413%   $184.4156   $184.42   $184.40   $184.40  
  7 purchase totals = $746.31       $790.2140   $790.21   $790.20   $790.20