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 $217.93   5.626%   $230.1907   $230.19   $230.20   $230.20  
  Purchase #2 $172.84   8.653%   $187.7958   $187.80   $187.80   $187.80  
  Purchase #3 $96.74   8.190%   $104.663   $104.66   $104.65   $104.70  
  Purchase #4 $124.91   7.836%   $134.6979   $134.70   $134.70   $134.70  
  Purchase #5 $227.40   3.103%   $234.4562   $234.46   $234.45   $234.50  
  Purchase #6 $26.53   12.817%   $29.9304   $29.93   $29.95   $29.90  
  Purchase #7 $10.74   5.581%   $11.3394   $11.34   $11.35   $11.30  
  7 purchase totals = $877.09       $933.0734   $933.08   $933.10   $933.10