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 $210.37   11.318%   $234.1797   $234.18   $234.20   $234.20  
  Purchase #2 $219.90   7.162%   $235.6492   $235.65   $235.65   $235.60  
  Purchase #3 $15.40   12.649%   $17.3479   $17.35   $17.35   $17.30  
  Purchase #4 $65.56   4.698%   $68.64   $68.64   $68.65   $68.60  
  Purchase #5 $205.97   11.616%   $229.8955   $229.90   $229.90   $229.90  
  Purchase #6 $196.46   4.410%   $205.1239   $205.12   $205.10   $205.10  
  Purchase #7 $28.26   4.269%   $29.4664   $29.47   $29.45   $29.50  
  7 purchase totals = $941.92       $1,020.3026   $1,020.31   $1,020.30   $1,020.20