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 $57.83   12.782%   $65.2218   $65.22   $65.20   $65.20  
  Purchase #2 $96.88   9.431%   $106.0168   $106.02   $106.00   $106.00  
  Purchase #3 $81.41   12.370%   $91.4804   $91.48   $91.50   $91.50  
  Purchase #4 $22.64   3.372%   $23.4034   $23.40   $23.40   $23.40  
  Purchase #5 $134.92   12.596%   $151.9145   $151.91   $151.90   $151.90  
  Purchase #6 $22.48   7.104%   $24.077   $24.08   $24.10   $24.10  
  Purchase #7 $11.32   3.424%   $11.7076   $11.71   $11.70   $11.70  
  7 purchase totals = $427.48       $473.8215   $473.82   $473.80   $473.80