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 $54.61   12.206%   $61.2757   $61.28   $61.30   $61.30  
  Purchase #2 $67.28   9.723%   $73.8216   $73.82   $73.80   $73.80  
  Purchase #3 $175.50   3.626%   $181.8636   $181.86   $181.85   $181.90  
  Purchase #4 $39.62   11.335%   $44.1109   $44.11   $44.10   $44.10  
  Purchase #5 $72.84   3.685%   $75.5242   $75.52   $75.50   $75.50  
  Purchase #6 $234.56   8.602%   $254.7369   $254.74   $254.75   $254.70  
  Purchase #7 $208.72   12.442%   $234.6889   $234.69   $234.70   $234.70  
  7 purchase totals = $853.13       $926.0218   $926.02   $926.00   $926.00