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 $212.97   10.167%   $234.6227   $234.62   $234.60   $234.60  
  Purchase #2 $187.54   7.355%   $201.3336   $201.33   $201.35   $201.30  
  Purchase #3 $53.37   5.523%   $56.3176   $56.32   $56.30   $56.30  
  Purchase #4 $209.52   4.814%   $219.6063   $219.61   $219.60   $219.60  
  Purchase #5 $65.73   12.719%   $74.0902   $74.09   $74.10   $74.10  
  Purchase #6 $162.75   8.732%   $176.9613   $176.96   $176.95   $177.00  
  Purchase #7 $123.71   13.353%   $140.229   $140.23   $140.25   $140.20  
  7 purchase totals = $1,015.59       $1,103.1607   $1,103.16   $1,103.15   $1,103.10