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 $62.52   8.414%   $67.7804   $67.78   $67.80   $67.80  
  Purchase #2 $228.64   7.293%   $245.3147   $245.31   $245.30   $245.30  
  Purchase #3 $86.30   12.334%   $96.9442   $96.94   $96.95   $96.90  
  Purchase #4 $119.71   10.502%   $132.2819   $132.28   $132.30   $132.30  
  Purchase #5 $119.81   5.213%   $126.0557   $126.06   $126.05   $126.10  
  Purchase #6 $168.91   5.203%   $177.6984   $177.70   $177.70   $177.70  
  Purchase #7 $175.95   5.640%   $185.8736   $185.87   $185.85   $185.90  
  7 purchase totals = $961.84       $1,031.9489   $1,031.94   $1,031.95   $1,032.00