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 $209.91   11.787%   $234.6521   $234.65   $234.65   $234.70  
  Purchase #2 $126.96   12.424%   $142.7335   $142.73   $142.75   $142.70  
  Purchase #3 $24.62   5.460%   $25.9643   $25.96   $25.95   $26.00  
  Purchase #4 $81.46   11.861%   $91.122   $91.12   $91.10   $91.10  
  Purchase #5 $7.68   8.455%   $8.3293   $8.33   $8.35   $8.30  
  Purchase #6 $169.42   7.357%   $181.8842   $181.88   $181.90   $181.90  
  Purchase #7 $242.36   6.551%   $258.237   $258.24   $258.25   $258.20  
  7 purchase totals = $862.41       $942.9224   $942.91   $942.95   $942.90