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 $65.72   12.756%   $74.1032   $74.10   $74.10   $74.10  
  Purchase #2 $146.72   11.131%   $163.0514   $163.05   $163.05   $163.10  
  Purchase #3 $206.64   6.449%   $219.9662   $219.97   $219.95   $220.00  
  Purchase #4 $232.85   13.833%   $265.0601   $265.06   $265.05   $265.10  
  Purchase #5 $84.57   13.179%   $95.7155   $95.72   $95.70   $95.70  
  Purchase #6 $198.50   3.850%   $206.1423   $206.14   $206.15   $206.10  
  Purchase #7 $125.91   4.257%   $131.27   $131.27   $131.25   $131.30  
  7 purchase totals = $1,060.91       $1,155.3087   $1,155.31   $1,155.25   $1,155.40