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 $218.78   12.671%   $246.5016   $246.50   $246.50   $246.50  
  Purchase #2 $203.28   4.307%   $212.0353   $212.04   $212.05   $212.00  
  Purchase #3 $76.65   11.737%   $85.6464   $85.65   $85.65   $85.60  
  Purchase #4 $120.82   13.609%   $137.2624   $137.26   $137.25   $137.30  
  Purchase #5 $244.54   10.331%   $269.8034   $269.80   $269.80   $269.80  
  Purchase #6 $125.58   7.329%   $134.7838   $134.78   $134.80   $134.80  
  Purchase #7 $229.52   4.146%   $239.0359   $239.04   $239.05   $239.00  
  7 purchase totals = $1,219.17       $1,325.0688   $1,325.07   $1,325.10   $1,325.00