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 $62.55   8.824%   $68.0694   $68.07   $68.05   $68.10  
  Purchase #2 $181.85   7.489%   $195.4687   $195.47   $195.45   $195.50  
  Purchase #3 $222.56   4.220%   $231.952   $231.95   $231.95   $232.00  
  Purchase #4 $60.67   6.383%   $64.5426   $64.54   $64.55   $64.50  
  Purchase #5 $111.77   12.798%   $126.0743   $126.07   $126.05   $126.10  
  Purchase #6 $16.33   6.225%   $17.3465   $17.35   $17.35   $17.30  
  Purchase #7 $120.54   9.831%   $132.3903   $132.39   $132.40   $132.40  
  7 purchase totals = $776.27       $835.8438   $835.84   $835.80   $835.90