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 $31.68   13.656%   $36.0062   $36.01   $36.00   $36.00  
  Purchase #2 $44.41   3.375%   $45.9088   $45.91   $45.90   $45.90  
  Purchase #3 $56.56   3.783%   $58.6997   $58.70   $58.70   $58.70  
  Purchase #4 $246.96   9.862%   $271.3152   $271.32   $271.30   $271.30  
  Purchase #5 $64.91   8.679%   $70.5435   $70.54   $70.55   $70.50  
  Purchase #6 $182.80   12.503%   $205.6555   $205.66   $205.65   $205.70  
  Purchase #7 $75.28   9.116%   $82.1425   $82.14   $82.15   $82.10  
  7 purchase totals = $702.60       $770.2714   $770.28   $770.25   $770.20