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 $64.82   13.128%   $73.3296   $73.33   $73.35   $73.30  
  Purchase #2 $227.73   8.694%   $247.5288   $247.53   $247.55   $247.50  
  Purchase #3 $39.64   13.143%   $44.8499   $44.85   $44.85   $44.80  
  Purchase #4 $224.58   3.158%   $231.6722   $231.67   $231.65   $231.70  
  Purchase #5 $26.26   13.752%   $29.8713   $29.87   $29.85   $29.90  
  Purchase #6 $161.35   12.120%   $180.9056   $180.91   $180.90   $180.90  
  Purchase #7 $210.33   6.512%   $224.0267   $224.03   $224.05   $224.00  
  7 purchase totals = $954.71       $1,032.1841   $1,032.19   $1,032.20   $1,032.10