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 $69.66   7.668%   $75.0015   $75.00   $75.00   $75.00  
  Purchase #2 $96.71   6.378%   $102.8782   $102.88   $102.90   $102.90  
  Purchase #3 $137.86   4.758%   $144.4194   $144.42   $144.40   $144.40  
  Purchase #4 $220.88   4.105%   $229.9471   $229.95   $229.95   $229.90  
  Purchase #5 $145.75   4.640%   $152.5128   $152.51   $152.50   $152.50  
  Purchase #6 $97.65   9.621%   $107.0449   $107.04   $107.05   $107.00  
  Purchase #7 $196.74   4.587%   $205.7645   $205.76   $205.75   $205.80  
  7 purchase totals = $965.25       $1,017.5684   $1,017.56   $1,017.55   $1,017.50