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 $224.54   7.620%   $241.6499   $241.65   $241.65   $241.60  
  Purchase #2 $171.37   11.727%   $191.4666   $191.47   $191.45   $191.50  
  Purchase #3 $113.90   6.774%   $121.6156   $121.62   $121.60   $121.60  
  Purchase #4 $134.37   6.479%   $143.0758   $143.08   $143.10   $143.10  
  Purchase #5 $48.52   6.362%   $51.6068   $51.61   $51.60   $51.60  
  Purchase #6 $246.69   9.195%   $269.3731   $269.37   $269.35   $269.40  
  Purchase #7 $23.34   12.351%   $26.2227   $26.22   $26.20   $26.20  
  7 purchase totals = $962.73       $1,045.0105   $1,045.02   $1,044.95   $1,045.00