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 $218.89   12.607%   $246.4855   $246.49   $246.50   $246.50  
  Purchase #2 $70.52   8.147%   $76.2653   $76.27   $76.25   $76.30  
  Purchase #3 $33.53   10.837%   $37.1636   $37.16   $37.15   $37.20  
  Purchase #4 $137.29   5.671%   $145.0757   $145.08   $145.10   $145.10  
  Purchase #5 $248.85   10.352%   $274.611   $274.61   $274.60   $274.60  
  Purchase #6 $37.58   11.150%   $41.7702   $41.77   $41.75   $41.80  
  Purchase #7 $234.84   6.102%   $249.1699   $249.17   $249.15   $249.20  
  7 purchase totals = $981.50       $1,070.5412   $1,070.55   $1,070.50   $1,070.70