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 $206.68   5.457%   $217.9585   $217.96   $217.95   $218.00  
  Purchase #2 $165.84   7.353%   $178.0342   $178.03   $178.05   $178.00  
  Purchase #3 $231.96   4.122%   $241.5214   $241.52   $241.50   $241.50  
  Purchase #4 $147.73   5.309%   $155.573   $155.57   $155.55   $155.60  
  Purchase #5 $56.58   3.705%   $58.6763   $58.68   $58.70   $58.70  
  Purchase #6 $71.56   10.375%   $78.9844   $78.98   $79.00   $79.00  
  Purchase #7 $38.88   7.671%   $41.8625   $41.86   $41.85   $41.90  
  7 purchase totals = $919.23       $972.6103   $972.60   $972.60   $972.70