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 $77.58   5.633%   $81.9501   $81.95   $81.95   $82.00  
  Purchase #2 $182.69   11.516%   $203.7286   $203.73   $203.75   $203.70  
  Purchase #3 $118.95   12.842%   $134.2256   $134.23   $134.25   $134.20  
  Purchase #4 $99.31   4.199%   $103.48   $103.48   $103.50   $103.50  
  Purchase #5 $206.77   13.446%   $234.5723   $234.57   $234.55   $234.60  
  Purchase #6 $51.85   3.545%   $53.6881   $53.69   $53.70   $53.70  
  Purchase #7 $44.72   12.594%   $50.352   $50.35   $50.35   $50.40  
  7 purchase totals = $781.87       $861.9967   $862.00   $862.05   $862.10