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 $32.80   7.812%   $35.3623   $35.36   $35.35   $35.40  
  Purchase #2 $186.46   3.858%   $193.6536   $193.65   $193.65   $193.70  
  Purchase #3 $151.94   8.805%   $165.3183   $165.32   $165.30   $165.30  
  Purchase #4 $157.99   4.558%   $165.1912   $165.19   $165.20   $165.20  
  Purchase #5 $119.45   4.668%   $125.0259   $125.03   $125.05   $125.00  
  Purchase #6 $134.67   13.505%   $152.8572   $152.86   $152.85   $152.90  
  Purchase #7 $187.79   13.201%   $212.5802   $212.58   $212.60   $212.60  
  7 purchase totals = $971.10       $1,049.9887   $1,049.99   $1,050.00   $1,050.10