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 $91.57   12.157%   $102.7022   $102.70   $102.70   $102.70  
  Purchase #2 $26.59   10.554%   $29.3963   $29.40   $29.40   $29.40  
  Purchase #3 $238.47   10.576%   $263.6906   $263.69   $263.70   $263.70  
  Purchase #4 $239.54   11.265%   $266.5242   $266.52   $266.50   $266.50  
  Purchase #5 $111.73   5.870%   $118.2886   $118.29   $118.30   $118.30  
  Purchase #6 $163.96   12.558%   $184.5501   $184.55   $184.55   $184.60  
  Purchase #7 $190.98   12.845%   $215.5114   $215.51   $215.50   $215.50  
  7 purchase totals = $1,062.84       $1,180.6634   $1,180.66   $1,180.65   $1,180.70