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 $69.81   10.610%   $77.2168   $77.22   $77.20   $77.20  
  Purchase #2 $38.74   13.514%   $43.9753   $43.98   $44.00   $44.00  
  Purchase #3 $10.28   7.792%   $11.081   $11.08   $11.10   $11.10  
  Purchase #4 $83.28   6.622%   $88.7948   $88.79   $88.80   $88.80  
  Purchase #5 $240.95   11.205%   $267.9484   $267.95   $267.95   $267.90  
  Purchase #6 $79.79   9.256%   $87.1754   $87.18   $87.20   $87.20  
  Purchase #7 $69.25   7.559%   $74.4846   $74.48   $74.50   $74.50  
  7 purchase totals = $592.10       $650.6763   $650.68   $650.75   $650.70