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 $233.29   12.378%   $262.1666   $262.17   $262.15   $262.20  
  Purchase #2 $221.35   11.753%   $247.3653   $247.37   $247.35   $247.40  
  Purchase #3 $138.37   12.146%   $155.1764   $155.18   $155.20   $155.20  
  Purchase #4 $49.46   13.219%   $55.9981   $56.00   $56.00   $56.00  
  Purchase #5 $76.68   12.755%   $86.4605   $86.46   $86.45   $86.50  
  Purchase #6 $17.82   9.227%   $19.4643   $19.46   $19.45   $19.50  
  Purchase #7 $216.72   10.490%   $239.4539   $239.45   $239.45   $239.50  
  7 purchase totals = $953.69       $1,066.0851   $1,066.09   $1,066.05   $1,066.30