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 $207.28   12.386%   $232.9537   $232.95   $232.95   $233.00  
  Purchase #2 $81.71   11.487%   $91.096   $91.10   $91.10   $91.10  
  Purchase #3 $174.39   12.646%   $196.4434   $196.44   $196.45   $196.40  
  Purchase #4 $19.44   12.666%   $21.9023   $21.90   $21.90   $21.90  
  Purchase #5 $248.73   9.603%   $272.6155   $272.62   $272.60   $272.60  
  Purchase #6 $219.52   12.553%   $247.0763   $247.08   $247.10   $247.10  
  Purchase #7 $163.93   13.614%   $186.2474   $186.25   $186.25   $186.20  
  7 purchase totals = $1,115.00       $1,248.3346   $1,248.34   $1,248.35   $1,248.30