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 $228.79   13.316%   $259.2557   $259.26   $259.25   $259.30  
  Purchase #2 $241.72   8.191%   $261.5193   $261.52   $261.50   $261.50  
  Purchase #3 $126.89   6.123%   $134.6595   $134.66   $134.65   $134.70  
  Purchase #4 $148.56   8.453%   $161.1178   $161.12   $161.10   $161.10  
  Purchase #5 $188.26   8.315%   $203.9138   $203.91   $203.90   $203.90  
  Purchase #6 $64.28   12.306%   $72.1903   $72.19   $72.20   $72.20  
  Purchase #7 $183.38   12.524%   $206.3465   $206.35   $206.35   $206.30  
  7 purchase totals = $1,181.88       $1,299.0029   $1,299.01   $1,298.95   $1,299.00