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 $55.33   3.631%   $57.339   $57.34   $57.35   $57.30  
  Purchase #2 $122.43   9.162%   $133.647   $133.65   $133.65   $133.60  
  Purchase #3 $17.70   3.798%   $18.3722   $18.37   $18.35   $18.40  
  Purchase #4 $169.56   3.401%   $175.3267   $175.33   $175.35   $175.30  
  Purchase #5 $240.97   9.745%   $264.4525   $264.45   $264.45   $264.50  
  Purchase #6 $173.34   13.309%   $196.4098   $196.41   $196.40   $196.40  
  Purchase #7 $20.73   10.796%   $22.968   $22.97   $22.95   $23.00  
  7 purchase totals = $800.06       $868.5152   $868.52   $868.50   $868.50