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 $219.62   8.771%   $238.8829   $238.88   $238.90   $238.90  
  Purchase #2 $238.49   13.859%   $271.5423   $271.54   $271.55   $271.50  
  Purchase #3 $53.33   9.830%   $58.5723   $58.57   $58.55   $58.60  
  Purchase #4 $226.32   4.312%   $236.0789   $236.08   $236.10   $236.10  
  Purchase #5 $155.77   7.541%   $167.5166   $167.52   $167.50   $167.50  
  Purchase #6 $5.68   11.764%   $6.3482   $6.35   $6.35   $6.30  
  Purchase #7 $230.94   11.586%   $257.6967   $257.70   $257.70   $257.70  
  7 purchase totals = $1,130.15       $1,236.6379   $1,236.64   $1,236.65   $1,236.60