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 $67.98   11.200%   $75.5938   $75.59   $75.60   $75.60  
  Purchase #2 $48.93   11.630%   $54.6206   $54.62   $54.60   $54.60  
  Purchase #3 $24.88   7.191%   $26.6691   $26.67   $26.65   $26.70  
  Purchase #4 $165.73   6.139%   $175.9042   $175.90   $175.90   $175.90  
  Purchase #5 $32.74   7.236%   $35.1091   $35.11   $35.10   $35.10  
  Purchase #6 $250.79   7.640%   $269.9504   $269.95   $269.95   $270.00  
  Purchase #7 $17.56   9.356%   $19.2029   $19.20   $19.20   $19.20  
  7 purchase totals = $608.61       $657.0501   $657.04   $657.00   $657.10