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 $69.88   7.446%   $75.0833   $75.08   $75.10   $75.10  
  Purchase #2 $108.92   9.579%   $119.3534   $119.35   $119.35   $119.40  
  Purchase #3 $182.59   13.754%   $207.7034   $207.70   $207.70   $207.70  
  Purchase #4 $6.95   9.677%   $7.6226   $7.62   $7.60   $7.60  
  Purchase #5 $235.82   11.215%   $262.2672   $262.27   $262.25   $262.30  
  Purchase #6 $109.25   13.376%   $123.8633   $123.86   $123.85   $123.90  
  Purchase #7 $209.88   12.297%   $235.6889   $235.69   $235.70   $235.70  
  7 purchase totals = $923.29       $1,031.5821   $1,031.57   $1,031.55   $1,031.70