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 $133.58   6.864%   $142.7489   $142.75   $142.75   $142.70  
  Purchase #2 $72.54   4.214%   $75.5968   $75.60   $75.60   $75.60  
  Purchase #3 $53.98   3.842%   $56.0539   $56.05   $56.05   $56.10  
  Purchase #4 $16.62   7.774%   $17.912   $17.91   $17.90   $17.90  
  Purchase #5 $125.93   12.791%   $142.0377   $142.04   $142.05   $142.00  
  Purchase #6 $233.48   11.154%   $259.5224   $259.52   $259.50   $259.50  
  Purchase #7 $210.79   9.492%   $230.7982   $230.80   $230.80   $230.80  
  7 purchase totals = $846.92       $924.6699   $924.67   $924.65   $924.60