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 $60.81   13.832%   $69.2212   $69.22   $69.20   $69.20  
  Purchase #2 $74.65   9.112%   $81.4521   $81.45   $81.45   $81.50  
  Purchase #3 $232.43   12.139%   $260.6447   $260.64   $260.65   $260.60  
  Purchase #4 $243.49   7.831%   $262.5577   $262.56   $262.55   $262.60  
  Purchase #5 $250.71   12.224%   $281.3568   $281.36   $281.35   $281.40  
  Purchase #6 $21.29   9.855%   $23.3881   $23.39   $23.40   $23.40  
  Purchase #7 $79.46   11.445%   $88.5542   $88.55   $88.55   $88.60  
  7 purchase totals = $962.84       $1,067.1748   $1,067.17   $1,067.15   $1,067.30