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 $39.44   11.556%   $43.9977   $44.00   $44.00   $44.00  
  Purchase #2 $90.52   13.623%   $102.8515   $102.85   $102.85   $102.90  
  Purchase #3 $242.91   6.645%   $259.0514   $259.05   $259.05   $259.10  
  Purchase #4 $162.52   13.499%   $184.4586   $184.46   $184.45   $184.50  
  Purchase #5 $13.26   3.537%   $13.729   $13.73   $13.75   $13.70  
  Purchase #6 $230.75   5.602%   $243.6766   $243.68   $243.70   $243.70  
  Purchase #7 $174.75   13.378%   $198.1281   $198.13   $198.15   $198.10  
  7 purchase totals = $954.15       $1,045.8929   $1,045.90   $1,045.95   $1,046.00