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 $122.74   7.509%   $131.9565   $131.96   $131.95   $132.00  
  Purchase #2 $56.96   8.412%   $61.7515   $61.75   $61.75   $61.80  
  Purchase #3 $245.30   5.291%   $258.2788   $258.28   $258.30   $258.30  
  Purchase #4 $150.77   8.220%   $163.1633   $163.16   $163.15   $163.20  
  Purchase #5 $184.45   4.714%   $193.145   $193.15   $193.15   $193.10  
  Purchase #6 $149.66   6.172%   $158.897   $158.90   $158.90   $158.90  
  Purchase #7 $31.52   12.216%   $35.3705   $35.37   $35.35   $35.40  
  7 purchase totals = $941.40       $1,002.5626   $1,002.57   $1,002.55   $1,002.70