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 $185.79   9.614%   $203.6519   $203.65   $203.65   $203.70  
  Purchase #2 $68.95   10.131%   $75.9353   $75.94   $75.95   $75.90  
  Purchase #3 $77.87   9.299%   $85.1111   $85.11   $85.10   $85.10  
  Purchase #4 $26.51   11.495%   $29.5573   $29.56   $29.55   $29.60  
  Purchase #5 $213.80   9.231%   $233.5359   $233.54   $233.55   $233.50  
  Purchase #6 $160.54   8.402%   $174.0286   $174.03   $174.05   $174.00  
  Purchase #7 $139.25   4.591%   $145.643   $145.64   $145.65   $145.60  
  7 purchase totals = $872.71       $947.4631   $947.47   $947.50   $947.40