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 $44.31   9.422%   $48.4849   $48.48   $48.50   $48.50  
  Purchase #2 $183.71   10.317%   $202.6634   $202.66   $202.65   $202.70  
  Purchase #3 $64.46   5.480%   $67.9924   $67.99   $68.00   $68.00  
  Purchase #4 $208.98   4.372%   $218.1166   $218.12   $218.10   $218.10  
  Purchase #5 $183.46   7.241%   $196.7443   $196.74   $196.75   $196.70  
  Purchase #6 $177.43   12.414%   $199.4562   $199.46   $199.45   $199.50  
  Purchase #7 $86.64   11.740%   $96.8115   $96.81   $96.80   $96.80  
  7 purchase totals = $948.99       $1,030.2693   $1,030.26   $1,030.25   $1,030.30