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 $48.73   11.495%   $54.3315   $54.33   $54.35   $54.30  
  Purchase #2 $155.92   12.467%   $175.3585   $175.36   $175.35   $175.40  
  Purchase #3 $240.25   8.450%   $260.5511   $260.55   $260.55   $260.60  
  Purchase #4 $69.98   11.643%   $78.1278   $78.13   $78.15   $78.10  
  Purchase #5 $91.39   5.689%   $96.5892   $96.59   $96.60   $96.60  
  Purchase #6 $141.31   10.233%   $155.7703   $155.77   $155.75   $155.80  
  Purchase #7 $213.99   10.872%   $237.255   $237.26   $237.25   $237.30  
  7 purchase totals = $961.57       $1,057.9834   $1,057.99   $1,058.00   $1,058.10