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 $208.32   8.251%   $225.5085   $225.51   $225.50   $225.50  
  Purchase #2 $10.69   11.659%   $11.9363   $11.94   $11.95   $11.90  
  Purchase #3 $140.79   6.185%   $149.4979   $149.50   $149.50   $149.50  
  Purchase #4 $69.75   3.783%   $72.3886   $72.39   $72.40   $72.40  
  Purchase #5 $230.43   7.192%   $247.0025   $247.00   $247.00   $247.00  
  Purchase #6 $197.62   5.190%   $207.8765   $207.88   $207.90   $207.90  
  Purchase #7 $157.62   3.463%   $163.0784   $163.08   $163.10   $163.10  
  7 purchase totals = $1,015.22       $1,077.2887   $1,077.30   $1,077.35   $1,077.30