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 $219.43   3.273%   $226.6119   $226.61   $226.60   $226.60  
  Purchase #2 $69.41   5.684%   $73.3553   $73.36   $73.35   $73.40  
  Purchase #3 $68.37   3.271%   $70.6064   $70.61   $70.60   $70.60  
  Purchase #4 $250.72   4.568%   $262.1729   $262.17   $262.15   $262.20  
  Purchase #5 $41.75   10.418%   $46.0995   $46.10   $46.10   $46.10  
  Purchase #6 $180.79   7.283%   $193.9569   $193.96   $193.95   $194.00  
  Purchase #7 $90.93   11.211%   $101.1242   $101.12   $101.10   $101.10  
  7 purchase totals = $921.40       $973.9271   $973.93   $973.85   $974.00