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 $118.30   5.267%   $124.5309   $124.53   $124.55   $124.50  
  Purchase #2 $243.46   7.842%   $262.5521   $262.55   $262.55   $262.60  
  Purchase #3 $23.59   13.800%   $26.8454   $26.85   $26.85   $26.80  
  Purchase #4 $195.84   5.215%   $206.0531   $206.05   $206.05   $206.10  
  Purchase #5 $12.95   4.149%   $13.4873   $13.49   $13.50   $13.50  
  Purchase #6 $242.57   3.691%   $251.5233   $251.52   $251.50   $251.50  
  Purchase #7 $84.65   7.706%   $91.1731   $91.17   $91.15   $91.20  
  7 purchase totals = $921.36       $976.1652   $976.16   $976.15   $976.20