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 $34.58   5.113%   $36.3481   $36.35   $36.35   $36.30  
  Purchase #2 $67.89   8.483%   $73.6491   $73.65   $73.65   $73.60  
  Purchase #3 $204.55   8.681%   $222.307   $222.31   $222.30   $222.30  
  Purchase #4 $223.35   11.381%   $248.7695   $248.77   $248.75   $248.80  
  Purchase #5 $95.67   7.644%   $102.983   $102.98   $103.00   $103.00  
  Purchase #6 $55.82   13.754%   $63.4975   $63.50   $63.50   $63.50  
  Purchase #7 $216.74   13.408%   $245.8005   $245.80   $245.80   $245.80  
  7 purchase totals = $898.60       $993.3547   $993.36   $993.35   $993.30